The interval between pregnancies and the risk of preeclampsia

The analysis of recurrence risk as an epidemiological tool

Recurrence risk provides information on the heterogeneity of risk in the population, and thus is useful for aetiological studies. While recurrence risk is observable in many areas of epidemiology, it is particularly accessible in the study of perinatal events. High recurrence rates of pregnancy problems suggest genetic causes, but can also reflect the presence of persistent environmental causes. Specific patterns of recurrence risk can provide further clues about the relative importance of genetic vs. environmental factors, for example through comparisons of recurring pregnancy problems in women who change their male partner and women who keep the same partner. Interpretation of recurrence risk is subject to confusion from bias and confounding, and some examples are discussed. In addition to providing information on causality, recurrence risk offers a means for more efficient design of aetiological studies.

Partner change and perinatal outcomes: a systematic review

Epidemiological studies suggest that partner change may affect perinatal outcomes in subsequent pregnancies. We conducted a systematic review on the association between paternity change and perinatal outcomes. We searched the literature in MEDLINE using keywords 'paternity', 'partner', 'pre-eclampsia', 'preterm birth', 'low birth weight', and 'birth defects' from 1966 to 2005. We identified 19 studies that examined the association between partner change and specific perinatal outcomes: 12 on pre-eclampsia or hypertension in pregnancy, three on birth defects, three on preterm birth, and two on low birthweight. Partner change was consistently associated with an increased risk of pre-eclampsia or hypertension in pregnancy in 11 of 12 studies (the unadjusted relative risk [RR] ranging from 1.2 to 8.3). However, after controlling for birth interval as a confounder in multivariate analysis, two studies using the same birth registry data showed a modestly reduced risk in relation to partner change (RR=0.84 and 0.73, respectively), while two studies found a slightly increased risk (both RR=1.3). Retrospective cohort studies presented inconsistent findings on the association between partner change and risk of preterm birth and low birthweight. Finally, three population-based cohort studies demonstrated that partner change significantly reduced the recurrence of the same or similar birth defects in subsequent births (RRs ranging from 0.1 to 0.76). We conclude that partner change reduces the risk of recurrent same birth defects. However, epidemiological evidence on the effect of partner change on pre-eclampsia, preterm birth and low birthweight is inconclusive. Whether birth interval should be controlled for in the association between partner change and pre-eclampsia warrants caution.

Recurrence of Ischemic Placental Disease

OBJECTIVE

To test the hypothesis that the presence of preeclampsia, small for gestational age (SGA)-birth, and placental abruption in the first pregnancy confers increased risk in the second pregnancy.

METHODS

A retrospective cohort study entailing a case-crossover analysis was performed based on women who had two consecutive singleton live births (n=154,810) between 1989 and 1997 in Missouri. Small for gestational age was defined as infants with birth weight below the 10th centile for gestational age. Risk and recurrence of ischemic placental disease was assessed from fitting logistic regression models after adjusting for several confounders.

RESULTS

Preeclampsia in the first pregnancy was associated with significantly increased risk of preeclampsia (odds ratio 7.03, 95% confidence interval 6.51, 7.59), SGA (odds ratio 1.16, 95% confidence interval 1.06, 1.27), and placental abruption (odds ratio 1.90, 95% confidence interval 1.51, 2.38) in the second pregnancy. Similarly, women with SGA and abruption in the first pregnancy were associated with increased risks of all other conditions in the second pregnancy.

CONCLUSION

Women with preeclampsia, SGA, and placental abruption in their first pregnancy--conditions that constitute ischemic placental disease--are at substantially increased risk of recurrence of any or all these conditions in their second pregnancy. Although causes of these conditions remain largely speculative, these entities may manifest through a common pathway of ischemic placental disease with significant risk of recurrence.

The effects and mechanisms of primiparity on the risk of pre-eclampsia: a systematic review

Pre-eclampsia has been dubbed as 'a disease of primiparity'. However, the effects and mechanisms of the association of primiparity with pre-eclampsia have not been clearly defined. We conducted a systematic review of studies evaluating the effect of primiparity on the risk of pre-eclampsia, and studies (published between January 1966 and July 2005) on the mechanisms underlying such an association. A total of 26 original studies were identified and a meta-analysis carried out for the risk of pre-eclampsia among primiparous vs. multiparous women. Variably (1.4-5.5 times) higher risks of pre-eclampsia were observed in primiparous women in all studies, with a summary odds ratio (OR) of 2.42 [95% CI 2.16, 2.71]. The adjusted ORs were larger than crude ORs in all but one study after various adjustments. Except for abundant epidemiological evidence in support of the immune maladaptation theory, only four original studies examined the actual mechanisms of such primiparity-associated risk. Two (small) studies suggested differences in immunological responses in the aetiology of pre-eclampsia in primiparous vs. multiparous women. Two recent studies indicated that differences in angiogenic factor profile or reactivity to insulin resistance in early pregnancy may explain the elevated pre-eclampsia risk in first pregnancies. In conclusion, primiparity is associated with approximately 2.4-fold elevated risk of pre-eclampsia. Although immune maladaptation is generally considered as the basis to explain such an elevated risk, few data are available on immune maladaptation parameters in primiparous vs. multiparous pregnancies. Available data are insufficient to interpret the mechanisms of such primiparity-associated excess risk of pre-eclampsia.

Partner change, birth interval and risk of pre-eclampsia: a paradoxical triangle

Immunology has been hypothesised to play a critical role in the development of pre-eclampsia. A number of epidemiological studies have shown that multiparous women who changed partner had an increased risk of pre-eclampsia in the following pregnancy compared with multiparous women with the same partner. However, partner change is often associated with a long birth interval. Two recent papers using data from the same birth registry reported that, after controlling for birth interval, partner change was associated with a reduced risk of pre-eclampsia. Based on a causal diagram, the author argues conceptually that birth interval is not a confounder but more likely to be a collider. Controlling for or stratifying birth interval in the association between partner change and risk of pre-eclampsia could be inappropriate and may have produced a spurious association.

Influence of parity on fetal mortality in prolonged pregnancy

OBJECTIVE

In England an estimated 50,000 inductions of labour at or beyond 41 weeks' gestation are conducted each year. However, the published evidence on the effect of parity on stillbirth in prolonged pregnancy is limited, and has produced conflicting data. The aim of this study is to evaluate the influence of parity on fetal mortality in prolonged pregnancies.

STUDY DESIGN

Retrospective analysis of 145,695 singleton births with known parity and no malformation noted at birth to residents in the former North-East Thames Region, UK. The parity and gestation specific stillbirth risks and relative risks per 1000 ongoing pregnancies were calculated in relation to parity between 37 and 45 weeks.

RESULTS

Before 41 weeks the stillbirth risk rose gradually but did not differ by parity. By 41 weeks there was a substantial increase in the stillbirth risk in nulliparous women but not in parous women. The pattern of rise is such that the stillbirth risk is 2.9 times higher (95% CI 1.06-8.19) in nulliparous women at >42 weeks' gestation.

CONCLUSION

Being parous appears to have a protective effect on fetal mortality in prolonged pregnancy. These findings question the need for routine induction of labour at 41 weeks in parous women.

Pre-eclampsia: Is the immune maladaptation hypothesis still standing? An epidemiological update

Despite much research, and clear improvement in our understanding of risk factors and pathogenetic mechanisms, the exact etiology of pre-eclampsia remains unknown. The immune maladaptation hypothesis has been challenged recently by several large epidemiological studies. One of the explanations for contradictory findings might be that the type of pre-eclampsia seen by obstetricians in developed countries mostly involves 30 and more years old, mildly obese pregnant women having near-term pre-eclampsia. It could be that this type of pre-eclampsia is primarily related to pre-existing maternal constitutional factors. This type of pre-eclampsia might be the dominant type of pre-eclampsia in the large Scandinavian and USA studies. In contrast, the epidemiology of pre-eclampsia in young women (age 15-25), so commonly seen in developing countries and certain lower socio-economic groups in developed countries, appears more in line with the immune maladaptation hypothesis. The aim here is to provide an updated review on studies supporting or challenging the immune maladaptation hypothesis.

Short interpregnancy interval and risk of spontaneous preterm delivery

OBJECTIVES

Short interpregnancy intervals are related to increased prevalence of adverse perinatal outcomes. However, the reported association with preterm birth might be due to confounding by factors such as previous pregnancy outcomes, socioeconomic level or lifestyles. The objective of this study was to evaluate the effect of short interpregnancy interval on the occurrence of spontaneous preterm delivery.

STUDY DESIGN

The prevalence of a short interpregnancy interval, defined as six or less months between a preceding delivery or abortion and the last menstrual period before index pregnancy, was compared between 263 spontaneous preterm (<37 weeks) and 299 term (37-42 weeks) consecutive births. Separate analyses were performed for early (<34 weeks) and late (34-36 weeks) preterm deliveries. Crude and adjusted odds ratios (ORs) and 95% confidence intervals (CI) were calculated using unconditional logistic regression.

RESULTS

There was a significant association between short interpregnancy interval and spontaneous early preterm delivery, both crude (OR=3.9; 95% CI: 1.91-8.10) and adjusted for maternal age, school education, previous birth outcomes, antenatal care, smoking habits, body mass index and gestational weight gain (adj(OR)=3.6; 95% CI: 1.41-8.98). No significant effect on spontaneous late preterm delivery was found (crude(OR)=0.8; 95% CI: 0.32-1.83).

CONCLUSIONS

This study showed that short interpregnancy intervals significantly increased the risk of early spontaneous preterm birth but no such effect was evident for late preterm deliveries.

Preeclampsia: a view through the danger model

Classical thinking suggests that the immune system undergoes activation on the basis of discrimination between 'self' and 'non-self'. Accordingly, the fetus activates the mother's immune system because the fetus is in part 'non-self'. Thus, successful pregnancy depends on constraint of maternal immunity. Preeclampsia is an outcome of lost constraint. Instead, the danger model suggests that normal pregnancy, regardless of the expression of 'non-self' antigens, does not activate the maternal immune system unless that pregnancy expresses danger signals. Thus, preeclampsia stems from stress or abnormal cell death in pregnancy-related tissues. This compels expression of specific danger signals and potential activation of anti-fetal immunity, which secondarily feeds the syndrome. Study of preeclampsia from this perspective may bring forth novel mechanisms and indicators of vascular and metabolic dysfunction during pregnancy.

Endometriosis is associated with a decreased risk of pre-eclampsia

BACKGROUND

We postulated that impaired endometrial differentiation in women with pelvic endometriosis predisposes for pre-eclampsia.

METHODS

A retrospective case-control study set at the University of Ghent IVF centre. The incidence of pre-eclampsia and pregnancy-induced hypertension (PIH) following the clinical and/or laparoscopic diagnosis of endometriosis-associated infertility (case group; n = 245 pregnancies) was compared with the incidence of these obstetric complications in pregnancies following treatment for male-factor infertility (control group; n = 274 pregnancies). Pregnancy data were obtained by searching electronic databases and postal questionnaires. The case and control groups were matched for age, parity and multiple pregnancies.

RESULTS

The incidence of pre-eclampsia was significantly lower in the case group (0.8%) when compared with control group (5.8%) (P = 0.002; odds ratio (OR) = 7.5, 95% confidence interval (CI): 1.7-33.3). Analysis of obstetric outcome in the subgroup of patients with laparoscopic data confirmed the lower risk of pre-eclampsia in the case (1.2%) versus control (7.4%) groups (P = 0.032; OR = 6.6, 95% CI: 1.2-37). PIH occurred in 3.5% and 8.7% of case and control pregnancies, respectively (P = 0.018; OR = 2.6, 95% CI: 1.2-6.0). The odds of developing pre-eclampsia were 5.67 times higher in the control group than in pregnancies following endometriosis-associated infertility. In multiple pregnancies, the odds of developing pre-eclampsia increased 1.93 times per additional child, with or without endometriosis.

CONCLUSIONS

We found no evidence that endometriosis predisposes for pre-eclampsia. Instead, the risk of hypertensive disorder in pregnancy is significantly reduced in women with endometriosis-associated infertility.

Effects of birth spacing on maternal health: a systematic review

The objective of the study was to explore the association between birth spacing and risk of adverse maternal outcomes. The study was a systematic review of observational studies that examined the relationship between interpregnancy or birth intervals and adverse maternal outcomes. Twenty-two studies met the inclusion criteria. Overall, long interpregnancy intervals, possibly longer than 5 years, are independently associated with an increased risk of preeclampsia. There is emerging evidence that women with long interpregnancy intervals are at increased risk for labor dystocia and that short intervals are associated with increased risks of uterine rupture in women attempting a vaginal birth after previous cesarean delivery and uteroplacental bleeding disorders (placental abruption and placenta previa). Less clear is the association between short intervals and other adverse outcomes such as maternal death and anemia. Long interpregnancy intervals are independently associated with an increased risk of preeclampsia. Both short and long interpregnancy intervals seem to be related to other adverse maternal outcomes, but more research is needed.

The role of the immune system in preeclampsia

Recent data demonstrate that an altered immune response may play a key role in the development of preeclampsia. Some epidemiological findings and animal models support this idea. In this article, we review the innate immune system and adaptive immune system in preeclampsia and discuss the pathophysiology of preeclampsia from an immunological viewpoint. The most characteristic immunological finding in preeclampsia is the activation of both the innate and adaptive immune system. Activated neutrophils, monocytes, and NK cells initiate inflammation which induce endothelial dysfunction, and activated T cells may support inadequate tolerance during pregnancy. The cytokine profile in preeclampsia shows that the production of type 1 cytokines, which induce inflammation, is dominant while the production of type 2 cytokines, which regulates inflammation, is suppressed. Furthermore, the immunoregulatory system is down-regulated in preeclampsia and persistent inflammation reduces regulatory T cell function. Therefore, systematical immunoactivation may be one cause of preeclampsia.

Novel risk factor in gastroschisis: Change of paternity

In recent years, an increase in the rate of gastroschisis has been documented in several countries throughout the world. Based on accumulating evidence that a maternal immunologic response to a novel set of paternal antigens may be involved in risk for several adverse pregnancy outcomes, including preeclampsia, reduced birth weight, and preterm delivery, we tested the hypothesis that a pregnancy following a change in fathers (change in paternity) may be a risk factor for gastroschisis. Using a case-control design, we compared the prevalence of change in paternity with the index pregnancy in 102 mothers of isolated gastroschisis cases to the prevalence of change in paternity in 117 mothers of non-malformed infants and 78 mothers of infants with neural tube defects or oral clefts. In a multivariate analysis, the adjusted odds of change in paternity in multigravid case mothers were 7.81 times higher (95% Confidence interval 2.80-21.88) relative to multigravid mothers of malformed and non-malformed controls combined, after adjustment for maternal age. These data suggest that maternal immune factors may play a role in the cause of gastroschisis. Further research is needed to corroborate these findings and to elucidate possible immunologic mechanisms involved in the pathogenesis of gastroschisis.

Increased insulin levels independent of gestational overweight in women with preeclampsia

BACKGROUND

The etiology of preeclampsia is unknown. It is controversial whether insulin resistance (IR) is present in preeclamptic patients, and it is unclear if hyperinsulinemia is dependent upon being overweight during pregnancy or on preeclampsia per se.

METHODS

We performed a cross-sectional study in 140 pregnant patients and compared serum insulin concentrations. These women, 18-40 years old, were classified into four groups: 1) overweight patients with mild preeclampsia (n = 21), 2) overweight patients without preeclampsia (n = 23), 3) non-overweight patients with mild preeclampsia (n = 48), and 4) non-overweight patients without preeclampsia (n = 48). An oral glucose tolerance test (OGTT) was performed in all patients between 29 and 40 weeks of gestation. Blood samples were taken at 0, 60, 120 and 180 min after 100 g oral glucose to measure serum glucose and insulin levels.

RESULTS

Basal and postload OGTT glucose values and basal insulin levels were similar in all groups. However, insulin levels at 60, 120 and 180 min were significantly higher (p = 0.009, p = 0.009, p = 0.046, respectively) in overweight patients with preeclampsia than in those without. Insulin levels at 60 and 180 min were also higher (p = 0.024, p = 0.023, respectively) in non-overweight patients with preeclampsia than in those without. The area under the curve (AUC) for glucose was not significantly different between both groups of overweight patients or between non-overweight patients with or without preeclampsia. In contrast, the AUC of insulin was significantly higher in preeclamptic patients in both overweight (p = 0.004) and non-overweight (p = 0.024) groups than in overweight and non-overweight groups without preeclampsia, respectively.

CONCLUSIONS

Increased insulin levels observed in mild preeclamptic patients were independent of overweight-related hyperinsulinemia.

Labor dystocia and its association with interpregnancy interval

OBJECTIVE

The purpose of this study was to evaluate the prevalence of labor dystocia and its association with interpregnancy interval.

STUDY DESIGN

We linked the birth data for Michigan infants who were born from 1994 to 2002 with the hospital discharge data. The International Classification of Diseases (9th revision, clinical modifications, ICD-9-CM) codes that indicate labor dystocia were identified by a physician panel and classified as functional and mechanical dystocia. We estimated the prevalence of labor dystocia and used stratified and logistic regression analyses to evaluate labor dystocia in relation to interpregnancy interval, controlling for other reproductive risk factors.

RESULTS

Overall, 20.8% of the births involved labor dystocia (11.1% functional; 12.5% mechanical). Both functional and mechanical dystocia were more prevalent in first births than in subsequent births; mechanical dystocia was more prevalent in multiple births than in singleton births. In singleton births to multiparous mothers, labor dystocia was associated with the interpregnancy interval in a dose-response fashion. Compared with an interpregnancy interval of <2 years, the adjusted odds ratios that was associated with interpregnancy intervals of 2 to 3, 4 to 5, 6 to 7, 8 to 9, and 10+ years were 1.06 (95% CI, 1.04-1.08), 1.15 (95% CI, 1.12-1.17), 1.25 (95% CI, 1.21-1.29), 1.31 (95% CI, 1.26-1.37), and 1.50 (95% CI, 1.45-1.56), respectively, when we controlled for other reproductive risk factors. Functional dystocia was associated more strongly with interpregnancy interval than mechanical dystocia.

CONCLUSION

Labor dystocia is common. In singleton births to multiparous mothers, labor dystocia increased with interpregnancy interval.

The incidence of pre-eclampsia among couples consisting of Japanese women and Caucasian men

Recent data from Hiby (2004) have suggested that a combination of maternal killer immunoglobulin receptor (KIR) AA genotype and fetal HLA-C2 genotype increases the risk of pre-eclampsia. Different human populations have a reciprocal relationship between KIR AA frequency and HLA-C2 frequency. Japanese people have highest frequency of KIR-AA alleles and lowest frequency of HLA-C2 alleles. However, Caucasians have a moderate frequency of KIR-AA and HLA-C2 alleles. If this hypothesis is correct, the incidence of pre-eclampsia among couples consisting of Japanese women and Caucasian men should be higher than that among couples consisting of Japanese women and Japanese men. Therefore, we investigated the incidence of pre-eclampsia among 324 couples consisting of Japanese women and Caucasian men. The incidence of pre-eclampsia in these couples consisting of Japanese women and Caucasian men was similar to that in Japanese women and Japanese men. Our data do not support that of Hiby et al. [Hiby, S.E., Walker, J.J., O'Shaughnessy, K.M., Redman, C.W.G., Carrington, M., Trowsdale, I., Moffett, A., 2004. Combinations of maternal KIR and fetal HLA-C genes influence the risk of pre-eclampsia and reproductive success. J. Exp. Med. 200, 957-965], although we did not check the haplotypes for HLA-C and KIR.

Previous cesarean delivery and risks of placenta previa and placental abruption

OBJECTIVE

To examine the association between cesarean delivery and previa and abruption in subsequent pregnancies.

METHODS

A retrospective cohort study of first 2 (n = 156,475) and first 3 (n = 31,102) consecutive singleton pregnancies using the 1989-1997 Missouri longitudinally linked data were performed. Relative risk (RR) was used to quantify the associations between cesarean delivery and risks of previa and abruption in subsequent pregnancies, after adjusting for several confounders.

RESULTS

Rates of previa and abruption were 4.4 (n = 694) and 7.9 (n = 1,243) per 1,000 births, respectively. The pregnancy after a cesarean delivery was associated with increased risk of previa (0.63%) compared with a vaginal delivery (0.38%, RR 1.5, 95% confidence interval [CI] 1.3-1.8). Cesarean delivery in the first and second births conferred a two-fold increased risk of previa in the third pregnancy (RR 2.0, 95% CI 1.3-3.0) compared with first two vaginal deliveries. Women with a cesarean first birth were more likely to have an abruption in the second pregnancy (0.95%) compared with women who had a vaginal first birth (0.74%, RR 1.3, 95% CI 1.2-1.5). Two consecutive cesarean deliveries were associated with a 30% increased risk of abruption in the third pregnancy (RR 1.3, 95% CI 1.0-1.8). A second pregnancy within a year after a cesarean delivery was associated with increased risks of previa (RR 1.7, 95% CI 0.9-3.1) and abruption (RR 1.5, 95% CI 1.1-2.3).

CONCLUSION

A cesarean first birth is associated with increased risks of previa and abruption in the second pregnancy. There is a dose-response pattern in the risk of previa, with increasing number of prior cesarean deliveries. A short interpregnancy interval is associated with increased risks of previa and abruption.

LEVEL OF EVIDENCE

II-2.

Influence of parity on first trimester endovascular trophoblast invasion

OBJECTIVE

To assess the effect of parity on endovascular trophoblastic invasion in early pregnancy.

DESIGN

Observational study.

SETTING

Teaching hospital.

PATIENT(S)

Healthy women at 10-14 weeks of gestation.

INTERVENTION(S)

Surgical termination of pregnancy for nonmedical reasons.

MAIN OUTCOME MEASURE(S)

Products of conception were blindly examined histologically with regard to the extent of decidual endovascular trophoblast invasion.

RESULT(S)

Samples were obtained from 20 nulliparous and 10 parous women. The presence of normal intradecidual endovascular trophoblast invasion was identified with a similar frequency in both groups (P=.28). However, the proportion of decidual vessels with endovascular trophoblast invasion was significantly higher in parous women (60%) compared with nulliparous women (32%, P<.001).

CONCLUSION(S)

Endovascular trophoblast invasion in early pregnancy is more extensive in parous women who already had an uncomplicated pregnancy than in nulliparous women.

Mechanisms of Disease: pre-eclampsia

Pre-eclampsia, a syndrome of pregnant women, is one of the leading causes of maternal and fetal morbidity and mortality. Despite active research, the etiology of this disorder remains an enigma. Recent work has, however, provided promising explanations for the causation of the disorder and some of its phenotypes. Evidence indicates that the symptoms of hypertension and proteinuria, upon which the diagnosis of pre-eclampsia is based, have several underlying causes. Nevertheless, the treatment of pre-eclampsia has not changed significantly in over 50 years. This review describes the most recent insights into the pathophysiology of pre-eclampsia from both basic and clinical research, and attempts to provide a unifying hypothesis to reconcile the abnormalities at the feto-placental level and the clinical features of the maternal syndrome. The novel findings outlined in this review provide a rationale for potential future prophylactic and therapeutic interventions for pre-eclampsia.

Recurrence risk in hyperemesis gravidarum

OBJECTIVES

To compare the risk of hyperemesis gravidarum in second pregnancies in women with and without hyperemesis in their first pregnancy, and to determine if this risk changes with changes in paternity or with the interval between deliveries.

DESIGN

Cohort study.

SETTING

Data from the population-based Medical Birth Registry of Norway, 1967-1998. Sample All women in the registry with records of their first and second singleton delivery, a total of 547,238 women.

METHODS

The relative risk of hyperemesis in the second delivery was estimated as odds ratios (ORs) in logistic regression models, controlling for potential confounding factors.

MAIN OUTCOME MEASURES

The main outcome measure was the risk of hyperemesis in the second pregnancy according to hyperemesis in the first pregnancy, interval between deliveries and change in paternity.

RESULTS

The risk of hyperemesis was 15.2% in the second pregnancy in women with and 0.7% in women without previous hyperemesis [OR=26.4, 95% confidence interval (CI) 24.2, 28.7]. The OR did not change after adjustment for maternal age, change in paternity, period of the first delivery and time interval between deliveries. After a change in paternity, the risk of recurrent hyperemesis was 10.9% compared with 16.0% in women without a change in paternity [adjusted OR (aOR)=0.60, 95% CI 0.39, 0.92]. The risk of hyperemesis in the second pregnancy increased with increasing time interval between deliveries, but only in women with no previous hyperemesis.

CONCLUSIONS

The primary finding was the high risk of recurrence observed in women with hyperemesis in the first pregnancy. The risk was reduced by a change in paternity. For women with no previous hyperemesis, a long interval between births slightly increased the risk of hyperemesis in the second pregnancy. Further studies are needed to explore the relative impact of genetic and environmental factors and their possible interactions in hyperemesis gravidarum.

Recurrence of pre-eclampsia across generations: exploring fetal and maternal genetic components in a population based cohort

OBJECTIVES

To assess the impact on risk of pre-eclampsia of genes that work through the mother, and genes of paternal origin that work through the fetus.

DESIGN

Population based cohort study.

SETTING

Registry data from Norway.

PARTICIPANTS

Linked generational data from the medical birth registry of Norway (1967-2003): 438,597 mother-offspring units and 286,945 father-offspring units.

MAIN OUTCOME MEASURES

Pre-eclampsia in the second generation.

RESULTS

The daughters of women who had pre-eclampsia during pregnancy had more than twice the risk of pre-eclampsia themselves (odds ratio 2.2, 95% confidence interval 2.0 to 2.4) compared with other women. Men born after a pregnancy complicated by pre-eclampsia had a moderately increased risk of fathering a pre-eclamptic pregnancy (1.5, 1.3 to 1.7). Sisters of affected men or women, who were themselves born after pregnancies not complicated by pre-eclampsia, also had an increased risk (2.0, 1.7 to 2.3). Women and men born after pre-eclamptic pregnancies were more likely to trigger severe pre-eclampsia in their own (or their partner's) pregnancy (3.0, 2.4 to 3.7, for mothers and 1.9, 1.4 to 2.5, for fathers).

CONCLUSIONS

Maternal genes and fetal genes from either the mother or father may trigger pre-eclampsia. The maternal association is stronger than the fetal association. The familial association predicts more severe pre-eclampsia.

Preeclampsia: a renal perspective

Preeclampsia is a syndrome that affects 5% of all pregnancies, producing substantial maternal and perinatal morbidity and mortality. The aim of this review is to summarize our current understanding of the pathogenesis of preeclampsia with special emphasis on the recent discovery that circulating anti-angiogenic proteins of placental origin may play an important role in the pathogenesis of proteinuria and hypertension of preeclampsia.

Assessment of risk for the development of pre-eclampsia by maternal characteristics and uterine artery Doppler

OBJECTIVE

To develop a method for the estimation of patient-specific risk for the development of pre-eclampsia by combining maternal history and uterine artery Doppler.

DESIGN

Prospective multicentre observational study.

SETTING

Antenatal clinics in seven hospitals in the UK and three overseas centres.

POPULATION

Unselected women with singleton pregnancies attending for routine antenatal care.

METHODS

Doppler studies of the uterine arteries were performed using colour flow mapping and pulsed wave Doppler at 23 weeks of gestation. The mean pulsatility index (PI) of the two uterine arteries was calculated. Doppler and maternal history variables were combined to develop a model for risk assessment. The incidence of pre-eclampsia was used to derive the prior risk for this complication. The posterior risk was derived by multiplying the prior odds with likelihood ratios (LRs) derived from independent risk factors identified from the maternal history, and the LR estimated from the heights of the frequency distributions of mean PI in affected and unaffected pregnancies.

MAIN OUTCOME MEASURE

Pre-eclampsia.

RESULTS

There were 17,480 women recruited to the study, in which 17,319 (99.1%) of these Doppler examination of both uterine arteries were completed, and outcome data were available in 16,806 (97.0%). Pre-eclampsia occurred in 369 (2.20%) cases. Significant independent prediction of pre-eclampsia was provided by mean PI, ethnic origin, body mass index (BMI), parity, cigarette smoking, history of hypertension and family or personal history of pre-eclampsia. Models were derived allowing calculation of patient-specific risk for development of pre-eclampsia. For a false-positive rate of 25%, the detection rate of pre-eclampsia by screening using maternal history was 45.3%, with uterine artery Doppler it was 63.1% and with combined assessment it was 67.5%.

CONCLUSIONS

Combining risk factors in the mother's history with Doppler of the uterine arteries allows calculation of patient-specific risk for the development of pre-eclampsia.

Maternal ethnicity, paternal ethnicity, and parental ethnic discordance: predictors of preeclampsia

OBJECTIVE

To examine the association of maternal and paternal ethnicity as well as parental ethnic discordance with preeclampsia.

METHODS

Retrospective cohort study of all low-risk women delivered from 1995 to 1999 within a mature managed care organization. Rates of preeclampsia were calculated for maternal, paternal, and combined ethnicity using both univariate and multivariate analyses.

RESULTS

Among the 127,544 low-risk women, when examining maternal ethnicity in a multivariate model controlling for maternal age, parity, education, and gestational age, we found that the rates of preeclampsia were higher among African American (5.2%; odds ratio [OR] 1.41, 95% confidence interval [CI] 1.25-1.62) women and lower among Latina (4.0%; OR 0.90, 95% CI 0.84-0.97) and Asian women (3.5%; OR 0.79, 95% CI 0.72-0.88), with all results being statistically significant as compared with white women. When paternal ethnicity was controlled for separately, however, the difference in the rate of preeclampsia among Asian women disappeared, the effect of African-American maternal ethnicity increased slightly (OR 1.49, 95% CI 1.33-1.72), and Asian paternity was found to be associated with the lowest rate of preeclampsia (3.2%; OR 0.76, 95% CI 0.68-0.85). Further, parental ethnic discordance was associated with an increase in the rate of preeclampsia (OR 1.13, 95% CI 1.02 - 1.26).

CONCLUSION

We found that rates of preeclampsia were lower with Asian paternal ethnicity. We also found that having a differing paternal and maternal ethnicity was associated with increased rates of preeclampsia. For every 1,000 pregnancies, there would be approximately 10 fewer cases of preeclampsia in the setting of Asian paternity and 5 more cases of preeclampsia in the setting of parental ethnic discordance. These differences may be useful in further investigation of the cause of preeclampsia.

LEVEL OF EVIDENCE

II-2.

Circulating levels of the antiangiogenic marker sFLT-1 are increased in first versus second pregnancies

Preeclampsia is far more common in women's first pregnancy but the mechanism of this association is unknown. Altered angiogenesis, marked by increased levels of circulating soluble fms-like tyrosine kinase (sFlt-1), an inhibitor of placental growth factor (PlGF) and vascular endothelial growth factor, has been implicated in the pathogenesis of preeclampsia. We tested the hypothesis that nulliparous women demonstrate increased sFlt-1 levels compared with multiparous women, suggesting an overall increase in relative antiangiogenesis during first pregnancies. We measured sFlt-1 and PlGF levels in early pregnancy serum samples from the first 2 completed pregnancies of 97 women who participated in the MOMS cohort study. Repeated measures analyses demonstrated that sFlt-1 levels were significantly increased in first compared with second pregnancies (877+/-598 pg/mL vs 728+/-399 pg/mL; P=.01) but there was no significant difference in PlGF levels (45.3+/-40.7 pg/mL vs 40.1+/-31.9 pg/mL; P=.14). After adjusting for age, gestational age, blood pressure, body mass index, smoking, and the interpregnancy time interval, the residual decrease in sFlt-1 levels from the first to the second pregnancy remained significant at 107 pg/mL (P=.04). Significant interaction between ethnicity and pregnancy order on sFlt-1 levels was observed such that Hispanic women demonstrated greater sFlt-1 levels than white women during their first pregnancy but lower levels in their second pregnancies. Increased sFlt-1 secretion in first versus second pregnancies may account in part for the increased risk of preeclampsia among nulliparous women. Additional studies are needed to verify these findings and to further examine ethnic differences in angiogenesis factors and their potential impact on the incidence of preeclampsia.

Indications of an altered immune balance in preeclampsia: A decrease in in vitro secretion of IL-5 and IL-10 from blood mononuclear cells and in blood basophil counts compared with normal pregnancy

It has been suggested that maladaptation of the maternal immune response during pregnancy might be a causal factor for preeclampsia. This study was designed to examine the systemic immune status at both the innate level and the adaptive level in pregnancies complicated by preeclampsia (n=15) and normal pregnancies (n=15). Spontaneous and in vitro-induced secretion of IL-5, IL-6, IL-10, IL-12, IL-13 and TNF-alpha, in response to paternal blood cells and the vaccination antigens purified protein derivate of tuberculin (PPD) and tetanus toxoid (TT), was detected in cell culture supernatants from blood mononuclear cells by ELISA. Preeclamptic women showed reduced numbers of basophil granulocytes in the blood (p=0.004) and lower spontaneous secretion of IL-5 from blood mononuclear cells (p=0.016). In addition, paternal antigen-induced secretion of IL-10 was decreased in preeclampsia compared with normal pregnancy (p=0.012). No further differences between preeclampsia and normal pregnancy were found for any stimuli or cytokines. The present findings of reduced basophil numbers and lower spontaneous in vitro secretion of IL-5 in preeclampsia compared with normal pregnancy indicate a decrease in systemic Th2 immunity in preeclampsia. Furthermore, the decrease in paternal antigen-induced secretion of the immunosuppressive cytokine IL-10 in preeclampsia indicates a fetus-specific decrease in immunosuppression mediated by blood mononuclear cells. Whether these systemic changes are a cause or a consequence of preeclampsia remains to be elucidated.

Soluble Fms-like tyrosine kinase 1 and endothelial dysfunction in the pathogenesis of preeclampsia

Preeclampsia, a pregnancy-specific syndrome of hypertension and proteinuria, is characterized by defective placental vasculogenesis and widespread maternal endothelial dysfunction. Although the manifestations of preeclampsia are primarily maternal, the burden of morbidity and mortality is often on the neonate, since the only effective treatment-delivery of the fetus and placenta-often results in iatrogenic prematurity. In this review, we summarize recent advances in our understanding of the pathophysiology of preeclampsia, including normal and aberrant placental vascular development and evidence for endothelial dysfunction. We describe recent evidence that supports a novel mechanism in which a maladaptive shift in placental production of angiogenic factors such as soluble fms-like tyrosine kinase 1 (a circulating antiangiogenic protein) may play an important role in the pathogenesis of preeclampsia.

Risk factors for pre-eclampsia at antenatal booking: systematic review of controlled studies

OBJECTIVE

To determine the risk of pre-eclampsia associated with factors that may be present at antenatal booking.

DESIGN

Systematic review of controlled studies published 1966-2002.

DATA SYNTHESIS

Unadjusted relative risks were calculated from published data.

RESULTS

Controlled cohort studies showed that the risk of pre-eclampsia is increased in women with a previous history of pre-eclampsia (relative risk 7.19, 95% confidence interval 5.85 to 8.83) and in those with antiphospholipids antibodies (9.72, 4.34 to 21.75), pre-existing diabetes (3.56, 2.54 to 4.99), multiple (twin) pregnancy (2.93, 2.04 to 4.21), nulliparity (2.91, 1.28 to 6.61), family history (2.90, 1.70 to 4.93), raised blood pressure (diastolic > or = 80 mm Hg) at booking (1.38, 1.01 to 1.87), raised body mass index before pregnancy (2.47, 1.66 to 3.67) or at booking (1.55, 1.28 to 1.88), or maternal age > or = 40 (1.96, 1.34 to 2.87, for multiparous women). Individual studies show that risk is also increased with an interval of 10 years or more since a previous pregnancy, autoimmune disease, renal disease, and chronic hypertension.

CONCLUSIONS

These factors and the underlying evidence base can be used to assess risk at booking so that a suitable surveillance routine to detect pre-eclampsia can be planned for the rest of the pregnancy.

Maternal and fetal genetic factors account for most of familial aggregation of preeclampsia: a population-based Swedish cohort study

There is accumulated evidence for genetic influences on preeclampsia. However, no study has been able to separate the effects of maternal and fetal genetic factors from environmental factors, and there are still uncertainties about the origin and magnitude of the genetic effects. We used the population-based Swedish Birth and Multi-Generation Registries to identify a cohort of women who gave birth from 1987 through 1997. In order to separate the genetic and environmental contributions to preeclampsia, we analyzed pregnancy outcomes from families joined by full siblings. We included information from 244,564 sibling pairs (62,236 sister pairs, 63,288 brother pairs, and 119,040 sister-brother pairs), who had 701,488 pregnancies. We found that 35% of the variance in liability of preeclampsia was attributable to maternal genetic effects, 20% to fetal genetic effects (with similar contribution of maternal and paternal genetic effects), 13% to the couple effect, less than 1% to shared sibling environment, and 32% to unmeasured factors. Among women and men without a history of preeclampsia, partner change reduced the risk of preeclampsia (odds ratio, 0.6; 95 percent confidence interval, 0.4-0.9). Genetic factors account for more than half of the liability of preeclampsia, and maternal genes contribute more than fetal genes. We suggest that the couple effect is due to a genetic interaction between mother and father.

The Influence of Pregnancy on Arterial Compliance

OBJECTIVE

To examine the effect of pregnancy and the interval between pregnancies on arterial compliance as measured by mean arterial pressure (MAP) and pulse pressure.

METHODS

We conducted a 3-month chart review of deliveries at a tertiary care hospital (index pregnancies). Data collected included demographics, obstetric history, blood pressures, prepregnancy weight, weight gain, and neonatal outcome. If a subject's first delivery occurred at our institution, these records were reviewed in a similar fashion. Mean antepartum MAP and pulse pressure were calculated and compared for each trimester between index and first pregnancies. Statistical methods employed included repeated measures analysis of variance, repeated measures analysis of covariance, and correlation analysis.

RESULTS

Two hundred eighty-five charts were reviewed. Forty-seven women had complete data covering both index and first pregnancy. Mean arterial pressure was significantly higher in all trimesters of first compared with index pregnancies (first pregnancy-first trimester 82.0 +/- 8.1 mm Hg, index pregnancy-first trimester 79.4 +/- 7.6 mm Hg, P = .032; first-second trimester 81.6 +/- 6.7 mm Hg, index-second trimester 78.7 +/- 6.6 mm Hg, P = .016; first-third trimester 83.9 +/- 6.9 mm Hg, index-third trimester 81.6 +/- 6.9 mm Hg, P = .047). Repeated measures analysis of covariance confirmed that pregnancy order contributed independently to differences in MAP. The interval between pregnancies was found to be inversely related to the difference in MAP from first to index pregnancies by trimester (r = -0.41, P = .004) and the change in MAP within pregnancy from first to third trimester (r = -0.31, P = .046).

CONCLUSION

Mean arterial pressure is reduced in subsequent pregnancies compared with first pregnancies. This raises the possibility that pregnancy plays a role in modifying cardiovascular compliance. Consistent with this, the effect has temporal limitations in that the shorter the interval between pregnancies, the greater the reduction in MAP.

Pre-eclampsia

Pre-eclampsia is a major cause of maternal mortality (15-20% in developed countries) and morbidities (acute and long-term), perinatal deaths, preterm birth, and intrauterine growth restriction. Key findings support a causal or pathogenetic model of superficial placentation driven by immune maladaptation, with subsequently reduced concentrations of angiogenic growth factors and increased placental debris in the maternal circulation resulting in a (mainly hypertensive) maternal inflammatory response. The final phenotype, maternal pre-eclamptic syndrome, is further modulated by pre-existing maternal cardiovascular or metabolic fitness. Currently, women at risk are identified on the basis of epidemiological and clinical risk factors, but the diagnostic criteria of pre-eclampsia remain unclear, with no known biomarkers. Treatment is still prenatal care, timely diagnosis, proper management, and timely delivery. Many interventions to lengthen pregnancy (eg, treatment for mild hypertension, plasma-volume expansion, and corticosteroid use) have a poor evidence base. We review findings on the diagnosis, risk factors, and pathogenesis of pre-eclampsia and the present status of its prediction, prevention, and management.

Organizing population data into complex family pedigrees: application of a second-order data linkage to state birth defects registries

Researchers and health officials are increasingly using electronic linkage of large-scale health data systems as a tool for assembling a comprehensive picture of birth defects at a population level. Current linkage and database techniques are limited to first-order linkage--linking information on a single individual in one database with information on that same individual in another database. For example, while current strategies may indicate whether a child with a certain birth defect also has a specific metabolic disorder or risk factor, they are unable to readily determine whether he or she also has any siblings or other relatives with the same pattern. In contrast, the current manuscript proposes a second-order linkage--one that organizes data so that individual-level data can readily be organized into families or extended family pedigrees across an entire population. The ability to link and organize population data into family pedigrees can have significant, broad impact upon health research and service delivery. This can lead to large-scale analysis of genetic factors and, with the linking of environmental data, the potential for large-scale studies of gene-environment interactions. In addition, it expands the potential for epidemiological research by readily allowing the examination of familial effects upon population rates of birth defects, and provides valuable information that can assist in applied public health. An example of a second order database incorporating an electronic birth defects registry is presented.

Recurrent preeclampsia and perinatal outcome: a study of women with recurrent preeclampsia compared with women with preeclampsia who remained normotensive during their prior pregnancies

OBJECTIVE

To evaluate the impact of preeclampsia recurrence on perinatal outcome.

MATERIALS AND METHODS

A case-controlled study was performed in multiparous women who developed preeclampsia in index pregnancy (n = 64). Among these, women who had preeclampsia in previous pregnancies (n = 21) were compared to those who remained normotensive during their prior pregnancies (n = 43). Maternal and fetal variables were compared. Multivariate logistic analyses were performed to examine the impact of preeclampsia recurrence on fetal loss, preterm delivery, small for gestational age (SGA) occurrence and respiratory distress syndrome adjusted for confounding variables.

RESULTS

No statistical significant difference was observed between the two groups in terms of age, delivery weeks, steroid use and laboratory markers. Fetal loss was higher in women with recurrent preeclampsia (19.0%) than in women with preeclampsia who had a normotensive pregnancy history (4.7%), with adjusted odds ratio (OR) of 5.77 [95% confidence interval (CI) 0.84-39.54].

CONCLUSION

Women with recurrent preeclampsia had a higher rate of perinatal loss compared to women with preeclampsia who were normotensive in their prior pregnancies.

Offspring sex ratio at population level versus early and late onset preeclampsia

Male dominance being higher at preterm than term delivery was described in a population-based study by Vatten and Skjaerven [Early Hum. Dev. 76 (2004) 47]. A so-called "reversion" and "cross-over" in the sex ratio took place in preeclamptic gestations. These phenomena occurred earlier and stronger when associated with perinatal mortality and are in line with the overripeness ovopathy concept.

The placental problem: linking abnormal cytotrophoblast differentiation to the maternal symptoms of preeclampsia

The placenta is a remarkable organ. In normal pregnancy its specialized cells (termed cytotrophoblasts) differentiate into various specialized subpopulations that play pivotal roles in governing fetal growth and development. One cytotrophoblast subset acquires tumor-like properties that allow the cells to invade the decidua and myometrium, a process that attaches the placenta to the uterus. The same subset also adopts a vascular phenotype that allows these fetal cells to breach and subsequently line uterine blood vessels, a process that channels maternal blood to the rest of the placenta. In the pregnancy complication preeclampsia, which is characterized by the sudden onset of maternal hypertension, proteinuria and edema, cytotrophoblast invasion is shallow and vascular transformation incomplete. These findings, together with very recent evidence from animal models, suggest that preeclampsia is associated with abnormal placental production of vasculogenic/angiogenic substances that reach the maternal circulation with the potential to produce at least a subset of the clinical signs of this syndrome. The current challenge is to build on this knowledge to design clinically useful tests for predicting, diagnosing and treating this dangerous disorder.

Is pre-eclampsia more than one disease?

OBJECTIVES

The clinical characteristics of pre-eclampsia (gestational hypertension and proteinuria) may represent separate pathogenetic conditions. Pre-eclampsia accompanied by restricted fetal growth may originate from abnormal implantation, and appropriate or high birthweights may indicate a mixture of conditions, ranging from mild pre-eclampsia with modest placental involvement to hypertensive conditions without placental disease.

DESIGN

Prospective, observational study.

SETTING

General population.

POPULATION

We used data from the Medical Birth Registry of Norway, a population-based registry that has recorded births since 1967. For this study, we used information on length of gestation and presence of pre-eclampsia among 1,679,205 singletons born between 1967 and 1998. Pre-eclampsia was diagnosed in 44,220 (2.6%) pregnancies.

METHODS

We studied the risk of pre-eclampsia in relation to standardised measures (z scores) of birthweight, adjusted for length of gestation, and stratified by term and preterm delivery. We also explored whether gestational diabetes was more prevalent in conjunction with preterm than term pre-eclampsia.

MAIN OUTCOME MEASURES

Pre-eclampsia diagnosed at term or preterm.

RESULTS

For pre-eclampsia diagnosed around term, there was a U-shaped association with birthweight. Compared with appropriate birthweights for gestation, the risk of term pre-eclampsia was more than fourfold higher (relative risk [RR] 4.5, 95% confidence interval [CI], 4.3 to 4.7) if the baby's birthweight was lower than two standard deviations under the mean. For birthweights three standard deviations or higher than the mean, pre-eclampsia was more than twice as likely (RR 2.6, 95% CI 2.2-2.9). In contrast, the risk of preterm pre-eclampsia displayed an L-shaped association with birthweight. Low birthweight (less than -2 standard deviations) was associated with greatly increased risk (RR 9.9, 95% CI 9.1-10.9), but for high birthweights (>or=3 standard deviations), there was no association with the risk of preterm pre-eclampsia (RR 1.2, 95% CI 0.7-2.1). The prevalence of gestational diabetes was three times (prevalence ratio 3.3, 95% CI 2.6-3.6) higher in preterm than term pre-eclampsia.

CONCLUSION

Whereas pre-eclampsia with preterm delivery associated with low birthweight may be caused by underlying placental abnormality, pre-eclampsia delivered at term may represent a mixture of conditions, ranging from mild pre-eclampsia with moderate placental affection to hypertensive conditions in pregnancy without placental dysfunction.

The importance of genetic and environmental effects for pre-eclampsia and gestational hypertension: a family study

OBJECTIVES

To determine the importance of genetic effects in the aetiology of pre-eclampsia and gestational hypertension and to investigate whether pre-eclampsia and gestational hypertension share genetic aetiology.

DESIGN

Individual record linkage between the population-based Swedish Multi-Generation and the Medical Birth Registers.

SETTING

Sweden.

POPULATION

1,188,207 births between 1987 and 1997 and their parents.

METHODS

Similarities in relatives were measured by the number of pairs concordant and discordant for disease, the odds ratio (OR) and tetrachoric correlations. Estimates of genetic and environmental effect for gestational hypertension, pre-eclampsia and pregnancy-induced hypertension were calculated from structural equation model fitting.

MAIN OUTCOME MEASURES

Pre-eclampsia and gestational hypertension.

RESULTS

Full sisters and mother-daughters were more similar for pre-eclampsia (OR 3.3, 95% confidence interval [CI] 3.0-3.6 and OR 2.6, 95% CI 1.6-4.3, respectively) than half-sisters (maternal half-sisters OR 1.4, 95% CI 0.9-2.2 and paternal half-sisters OR 1.0, 95% CI 0.6-1.6). Full sisters and mother-daughters were also more similar for gestational hypertension than half-sisters. A full sister to a woman with pre-eclampsia also had a significantly increased risk of gestational hypertension (OR 2.5, 95% CI 2.2-2.8). In contrast, the risk for half-sisters was not increased. Model fitting suggested heritability estimates for pre-eclampsia of 31%, for gestational hypertension 20% and for pregnancy-induced hypertension 28%.

CONCLUSIONS

There is a genetic component in the development of pre-eclampsia and gestational hypertension and the pattern of co-morbidity suggests that they may share part of their genetic aetiology. This could be important for studies of potential susceptibility genes for these diseases.

Offspring sex and pregnancy outcome by length of gestation

BACKGROUND

It takes a higher number of male than female embryos to produce a live born infant. The unbalanced pregnancy survival by offspring sex may also be reflected in higher proportion of preterm male births, and in unbalanced sex distribution in certain pregnancy conditions, such as preeclampsia.

METHODS

We used data from the Medical Birth Registry of Norway, a population-based registry that has recorded births since 1967. For this study, we used information on offspring sex and length of gestation that was available for 1691053 (92.8%) singleton births among a total of 1822982 births from 1967 to 1998. We estimated sex ratios and perinatal mortality by length of gestation, and assessed whether the ratio of offspring sex in preeclampsia varied by length of gestation.

RESULTS

For preterm births, there was a strong male dominance. Within five categories of gestational age between 16 and 36 weeks, the male/female ratios were 2.48, 1.26, 1.28, 1.32, and 1.28. At weeks 37-39, the sex ratio was 1.17, but at weeks 40-42 the number of male and female births was practically identical (sex ratio 1.00). Over all, the male/female ratio was 1.06. Perinatal mortality was consistently higher in males across the whole range of gestational age; in total it was 21% (95% CI, 18-25%) higher in male offspring. In preeclampsia with preterm delivery (<37 weeks), the sex ratio was reversed: female offspring was substantially more common than males (sex ratio 0.87), but in preeclampsia with delivery at term (37-42 weeks), the proportion of males was higher (sex ratio 1.06) than for females.

CONCLUSION

The sex differences by length of gestation and in preeclampsia may reflect that male embryos are subject to stronger intrauterine selection forces than females. Possibly, implantation may be the critical event, where offspring sex may be one of the factors that determine success.

Preeclampsia and eclampsia in parturients from the in vitro fertilization program

Women from in vitro fertilization program are at higher risk for developing pregnancy induced hypertension, so we analyzed the incidence of preeclampsia and eclampsia in women who conceived in an in vitro fertilization program. A seven-year study included 144 parturients from in vitro fertilization program. The control group consisted of 39.112 parturients from general population. We analyzed only women with singleton pregnancies. There were 2.08% parturients from the in vitro fertilization program, and 0.40% from the control group, with diagnosis of preeclampsia, withc2=6,24; p0,10). Parturients from in vitro fertilization program are at statistically significantly higher risk for preeclampsia, but not for eclampsia, when compared with women from general population.

Effects on pregnancy outcome of changing partner between first two births: prospective population study

OBJECTIVE

To compare the effects on pregnancy outcomes of changing partner between the first two births with having the same partner for both births.

DESIGN

Prospective population study.

SETTING

Norway.

PARTICIPANTS

31 683 women who changed partner between their first two births and 456 458 women with the same partner for both births.

RESULTS

After adjustment for maternal age and education, interval between births, and decade of birth, the risk of adverse pregnancy outcomes for the second birth was higher for women who changed partner between the first two births compared with those who had the same partner for both births: preterm birth (< 37 weeks; relative risk 2.0, 95% confidence interval 1.9 to 2.1), low birth weight (< 2500 g; 2.5, 2.3 to 2.6), and infant mortality (1.8, 1.6 to 2.1). For the first birth, the risk of these adverse pregnancy outcomes was only slightly higher for mothers who subsequently had a second birth with another partner.

CONCLUSION

Women who change partner between their first two births are at an increased risk of delivering a preterm, low birthweight baby with an increased risk of infant mortality compared with women who have the same partner for both births.

The birth interval hypothesis-does it really indicate the end of the primipaternity hypothesis

Recent Norwegian data suggest the presence of a causal relationship between prolonged birth intervals and the risk for preeclampsia in subsequent pregnancies. It has been proposed that the birth interval data explain the known association between a change in paternity and the risk for preeclampsia. In this review, the authors explore alternative explanations for the Norwegian findings, and as such argue that there is currently no reason to reject the primipaternity hypothesis.