The impact of inter-pregnancy interval on subsequent risk of preterm birth

OBJECTIVE

The aim of the study was to assess optimal time to conceive after previous delivery associated with smallest risk of preterm birth.

METHODS

We selected all women (n = 2723) with their first and second singleton delivery between the years 2004 and 2012. Inter-pregnancy interval was defined as that between live birth and subsequent conception. We performed logistic regression analyses to assess the risk of preterm birth adjusted for maternal age and body mass index.

RESULTS

Association between inter-pregnancy interval and the natural logarithm of the adjusted relative risk of preterm birth had a J-shaped curve with lowest risk at 15 months after last birth.

CONCLUSION

The optimal time to conceive after a previous delivery is 15 months, as longer or shorter interval are associated with increased risk of preterm birth. Women with short or long inter-pregnancy intervals were 1.6 times more likely to experience preterm birth.

The effect of gestational diabetes, pre-gravid maternal obesity, and their combination ('diabesity') on outcomes of singleton gestations

OBJECTIVE

To assess the effect of the combination of gestational diabetes mellitus (GDM) and pre-gravid obesity ('diabesity') in singleton gestations.

METHODS

We compared perinatal outcomes of singleton gestations in mothers with GDM and pre-gravid obesity, with GDM but with normal pre-gravid BMI, and obese mothers without GDM.

RESULTS

We compared diabesity mothers (n = 1525, 24.4% of mothers with GDM, 9.9% of all obese women) to mothers with GDM but with normal BMI (n = 4704, 75.6% of mothers with GDM) and to obese mothers without GDM (n = 13,937, 90.1% of all obese mothers). Obesity, with and without GDM, increased the odds of having chronic hypertension whereas preeclampsia appears to be influenced by obesity only, as were the risk of births at <33 weeks' gestation, of birth weight >4000 g, low 5-min Apgar scores and NICU admissions.

CONCLUSION

Obesity (without diabetes) is more frequently associated with adverse perinatal outcomes than diabesity or GDM in non-obese mothers. A campaign to decrease pre-gravid obesity should have at least the same priority as any campaign to control GDM.

Respiratory morbidity in twins by birth order, gestational age and mode of delivery

OBJECTIVE

To evaluate the relationship between respiratory morbidity in twins by gestational age, birth order and mode of delivery.

METHODS

All twin deliveries at <37 weeks, registered in a national database, in the period 2003-2012 were classified into four gestational age groups: 33-36, 30-32, 28-29, and <28 weeks. Outcome variables included transient tachypnea of the newborn (TTN), respiratory distress syndrome (RDS) and need for assisted ventilation.

RESULTS

A total of 1836 twins were born vaginally, and 2142 twins were born by cesarean delivery, for a grand total of 3978 twins. TTN did not appear to be related to birth order and to the mode of delivery. In contrast, RDS was more frequent among the second born twins in the vaginal birth groups born at 30-36 weeks [odds ratio (OR) 2.5, 95% confidence interval (CI) 1.2-5.1 and OR 2.0, 95% CI 1.2-3.5 for 33-36 weeks and 30-32 weeks, respectively], whereas this trend was seen in the cesarean birth groups born earlier (OR 3.8, 95% CI 1.1-13.0 for 28-29 weeks). Cesarean delivery significantly increased the frequency of RDS in twin A as well as in twin B compared with vaginal birth, but only at gestational ages <30 weeks.

CONCLUSION

Mode of delivery and birth order have a gestational age dependent effect on the incidence of RDS.

Outcome of small for gestational age preterm singletons: a population-based cohort study

OBJECTIVE

To examine the outcomes of births among small and appropriate for gestational age (SGA and AGA) infants by gestational age and maternal characteristics.

MATERIALS AND METHODS

We used a national perinatal registry to compare the selected maternal and neonatal outcomes between AGA and SGA neonates born at gestational age groups 33-36, 30-32, 28-29, and <28 weeks. We evaluated maternal body mass index (BMI), pre-gestational/gestational diabetes, hypertensive disorders, and cesarean births as well as frequencies of 5-min Apgar score <7, intraventricular hemorrhage (IVH), respiratory distress syndrome (RDS), the need for assisted ventilation, and early neonatal deaths.

RESULTS

We evaluated 159,774 AGA (8871 preterm) and 13,735 SGA (1147 preterm) infants and found a gradual decrease in the incidence of SGA infants with increasing gestational age. Diabetes was unrelated to having an SGA or AGA infant among preterm births, but the odds ratio (OR) for preeclampsia among preterm-SGA pregnancies was up to 6.9 (95% CI 3.8, 12.5) at <28 weeks. SGA infants fare worse compared to AGA neonates in every parameter tested but only in preterm births >30 weeks.

CONCLUSIONS

Being SGA further complicates preterm births after 30 weeks of gestation but not earlier. This might suggest that an extended period in the hostile intrauterine environment, or that being born at <30 weeks, is bad enough and is not further aggravated by being SGA.

Outcome of monochorionic-biamniotic twins conceived by assisted reproduction: a population-based study

Objecive: To evaluate the perinatal outcome of monochorionic-diamniotic twins conceived by assisted reproduction technology (ART).

METHODS

We compared data from a national population-based perinatal registry on perinatal outcomes of monochorionic-diamniotic twins conceived by ART with their dichorionic counterparts and with spontaneous monochorionic-diamniotic twins. We compared maternal characteristics, pregnancy complications and perinatal outcomes.

RESULTS

Monochorionic-diamniotic twin pregnancies (n=45) comprised 5.5% of all ART twins, and 9.3% of all monochorionic twins in this dataset. ART does not appear to increase the already high risk of monochorionicity compared to spontaneous conception, with the latter having an increased incidence for birth weight <1500 g [odds ratio (OD) 2.6, 95% confidence interval (CI) 1.2-5.4].

CONCLUSION

Our results disagree with hospital-based data and suggest that monochorionic-diamniotic twins following ART are not at increased risk of adverse perinatal outcomes compared to spontaneous monochorionic-diamniotic twins as well as to dichorionc twins conceived by ART.

Cross-Country Individual Participant Analysis of 4.1 Million Singleton Births in 5 Countries with Very High Human Development Index Confirms Known Associations but Provides No Biologic Explanation for 2/3 of All Preterm Births

BACKGROUND

Preterm birth is the most common single cause of perinatal and infant mortality, affecting 15 million infants worldwide each year with global rates increasing. Understanding of risk factors remains poor, and preventive interventions have only limited benefit. Large differences exist in preterm birth rates across high income countries. We hypothesized that understanding the basis for these wide variations could lead to interventions that reduce preterm birth incidence in countries with high rates. We thus sought to assess the contributions of known risk factors for both spontaneous and provider-initiated preterm birth in selected high income countries, estimating also the potential impact of successful interventions due to advances in research, policy and public health, or clinical practice.

METHODS

We analyzed individual patient-level data on 4.1 million singleton pregnancies from four countries with very high human development index (Czech Republic, New Zealand, Slovenia, Sweden) and one comparator U.S. state (California) to determine the specific contribution (adjusting for confounding effects) of 21 factors. Both individual and population-attributable preterm birth risks were determined, as were contributors to cross-country differences. We also assessed the ability to predict preterm birth given various sets of known risk factors.

FINDINGS

Previous preterm birth and preeclampsia were the strongest individual risk factors of preterm birth in all datasets, with odds ratios of 4.6-6.0 and 2.8-5.7, respectively, for individual women having those characteristics. In contrast, on a population basis, nulliparity and male sex were the two risk factors with the highest impact on preterm birth rates, accounting for 25-50% and 11-16% of excess population attributable risk, respectively (p<0.001). The importance of nulliparity and male sex on population attributable risk was driven by high prevalence despite low odds ratios for individual women. More than 65% of the total aggregated risk of preterm birth within each country lacks a plausible biologic explanation, and 63% of difference between countries cannot be explained with known factors; thus, research is necessary to elucidate the underlying mechanisms of preterm birth and, hence, therapeutic intervention. Surprisingly, variation in prevalence of known risk factors accounted for less than 35% of the difference in preterm birth rates between countries. Known risk factors had an area under the curve of less than 0.7 in ROC analysis of preterm birth prediction within countries. These data suggest that other influences, as yet unidentified, are involved in preterm birth. Further research into biological mechanisms is warranted.

CONCLUSIONS

We have quantified the causes of variation in preterm birth rates among countries with very high human development index. The paucity of explicit and currently identified factors amenable to intervention illustrates the limited impact of changes possible through current clinical practice and policy interventions. Our research highlights the urgent need for research into underlying biological causes of preterm birth, which alone are likely to lead to innovative and efficacious interventions.

Embryo quality predictive models based on cumulus cells gene expression

Since the introduction of in vitro fertilization (IVF) in clinical practice of infertility treatment, the indicators for high quality embryos were investigated. Cumulus cells (CC) have a specific gene expression profile according to the developmental potential of the oocyte they are surrounding, and therefore, specific gene expression could be used as a biomarker. The aim of our study was to combine more than one biomarker to observe improvement in prediction value of embryo development. In this study, 58 CC samples from 17 IVF patients were analyzed. This study was approved by the Republic of Slovenia National Medical Ethics Committee. Gene expression analysis [quantitative real time polymerase chain reaction (qPCR)] for five genes, analyzed according to embryo quality level, was performed. Two prediction models were tested for embryo quality prediction: a binary logistic and a decision tree model. As the main outcome, gene expression levels for five genes were taken and the area under the curve (AUC) for two prediction models were calculated. Among tested genes, AMHR2 and LIF showed significant expression difference between high quality and low quality embryos. These two genes were used for the construction of two prediction models: the binary logistic model yielded an AUC of 0.72 ± 0.08 and the decision tree model yielded an AUC of 0.73 ± 0.03. Two different prediction models yielded similar predictive power to differentiate high and low quality embryos. In terms of eventual clinical decision making, the decision tree model resulted in easy-to-interpret rules that are highly applicable in clinical practice.

Hypertensive disorders during monozygotic and dizygotic twin gestations: A population-based study

OBJECTIVE

To determine whether the incidence of hypertensive disorders is different in monozygotic compared to dizygotic twin pregnancies.

METHODS

A registry-based survey of twin pregnancies delivered during 2003 to 2012. We used the best clinical estimate of zygosity based on the concept that all monochorionic twins are monozygotic and all unlike-sex pairs are dizygotic, thus excluding same-sex dichorionic twin gestations for which zygosity cannot be ascertained on clinical grounds. Study cohorts were twin pregnancies with or without preeclampsia and gestational hypertension.

RESULTS

A total of 3419 twin gestations met the inclusion criteria, of which 442 (12.9%) were monochorionic and 1255 (36.7%) were unlike-sex twins, excluding 1722 same-sex dichorionic twin gestations (50.4%). There was no significant difference in the incidence of preeclampsia (OR: 0.9; 95% CI: 0.4-2.0 for monozygotic males and OR: 0.6; 95% CI: 0.3-1.4 for monozygotic females) and gestational hypertension (OR: 0.7; 95% CI: 0.2-2.5 for monozygotic males, and OR: 0.7; 95% CI: 0.2-2.3 for monozygotic females) between monochorionic and unlike-sex pairs. Maternal prepregnancy obesity and nulliparity were the only significant associated factors of preeclampsia (OR: 3.8; 95% CI: 2.0-7.0, and OR: 2.5; 95% CI: 1.4-4.4, respectively). Maternal prepregnancy obesity (OR: 5.5; 95% CI: 2.5-12.2), maternal age ≥36 years (OR: 2.5; 95% CI: 1.1-6.1), and family history of hypertension (OR: 2.6; 95% CI: 1.3-5.1) were significantly associated with gestational hypertension.

CONCLUSION

Based on a large population-based dataset and on the best clinical estimate of twin zygosity, it appears that zygosity is not associated with hypertensive disorders in twin gestations.

Changes in incidence of iatrogenic and spontaneous preterm births over time: a population-based study

OBJECTIVE

To examine the proportion of iatrogenic births among all preterm births over a 26-year period.

PATIENTS AND METHODS

A registry-based survey of preterm deliveries between 1987 and 2012 analyzed by the onset of labor: spontaneous with intact membranes, preterm premature rupture of membranes (PPROM) or iatrogenic. Stratification into categories by gestation (22 weeks to 27 weeks and 6 days, 28 weeks to 31 weeks and 6 days, 32 weeks to 33 weeks and 6 days, 34 weeks to 36 weeks and 6 days) was performed. Preterm birth rates were analyzed using the Mantel-Haenszel linear-by-linear association χ2-test (P<0.05 significant). Logistic regression was used to account for potential confounders.

RESULTS

Overall preterm birth rate was 5.9% (31328 deliveries) including 2358 (0.4%) before 28 completed weeks, 3388 (0.6%) between 28 weeks and 31 weeks 6 days, 3970 (0.8%) between 32 weeks and 33 weeks and 6 days, and 21611 (4.1%) between 34 weeks and 36 weeks and 6 days There was an increase in overall preterm birth rate (P<0.001). The rate of iatrogenic preterm births and PPROM increased over time (P<0.001 and P<0.014, respectively). Rates of spontaneous preterm birth decreased (P<0.001). After accounting for potential confounders, year of birth remained an independent risk factor for iatrogenic preterm delivery in all four gestational age categories (P<0.001).

CONCLUSION

The incidence of iatrogenic preterm birth is increasing with a concomitant decrease in the incidence of spontaneous preterm birth. Attempts to analyze, interpret and decrease preterm birth rates should consider spontaneous and iatrogenic preterm births separately.

Growth curves for twins in Slovenia

Abnormalities of fetal growth are more common in twins. We introduce the growth curves for monitoring fetal growth in twin pregnancies in Slovenia. Slovenian National Perinatal Information System for the period between 2002 and 2010 was used to calculate birth weight percentiles for all live born twins for each week from 22nd to 40th week. The calculated percentiles of birth weight for all live-born twins in Slovenia served as the basis for drawing 'growth' curves. The calculated growth curves for twins will help accurately diagnose small or large twin fetuses for their gestational age in the native central European population.

A population-based comparison between actual maternal weight gain and the Institute of Medicine weight gain recommendations in singleton pregnancies

OBJECTIVE

To compare the actual maternal weight gain to that recommended by the Institute of Medicine (IOM) in term singleton gestations.

METHODS

We used data from the Slovenian National Perinatal Information System to select singleton pregnancies born at ≥38 weeks during the period from 2003 to 2012. We calculated the frequencies of mothers who gained less than, more than, and as recommended by the IOM according to their pregravid body mass index (BMI). We also compared the fetal size parameters in under- and over-gainer to those who gained weight as recommended by the IOM.

RESULTS

We selected 173,715 patients who delivered at ≥38 weeks. Of these patients, the recommended weight gain was achieved by 56,868 (32.7%, 95% CI 32.5, 32.9) only, 82,617 (47.6%, 95% CI 47.3, 47.8) were over-gainers, and 34,230 (19.7%, 95% CI 19.5, 19.8) gained less than recommended. Neither undergaining nor overgaining were always synonymous with adverse fetal outcomes.

CONCLUSIONS

Roughly two-thirds of singleton mothers did not gain weight during pregnancy according to the IOM recommendations. Inappropriate maternal weight gain, however, was not always associated with adverse fetal outcomes and this implies that a tailored approach rather than strict adherence to the IOM recommendations may be more practical.

The relationship between cesarean section rate in term singleton pregnancies, maternal weight, and weight gain during pregnancy

OBJECTIVE

Pregravid maternal weight and appropriate weight gain during pregnancy might be associated with increased cesarean section rate.

STUDY DESIGN

We used data from the Slovenian National Perinatal Information System to select singleton pregnancies born at ≥38 weeks, during the period between 2003 and 2012. We calculated the frequencies of urgent and elective cesarean sections (UCS and ECS, respectively) in mothers who gained less than, more than, and as recommended by the Institute of Medicine (IOM) according to their pregravid body mass index (BMI).

RESULTS

The analysis included 170,121 women who delivered singletons ≥38 weeks. A total of 24,327 (14.3%) women underwent cesarean section: 14,692 (8.6%) UCS and 9635 (5.7%) ECS. The frequency of cesareans, both UCS and ECS, increases as BMI increases irrespective of weight gain pattern. The frequency of urgent cesareans in all women increases and that of elective cesareans among obese women decreases as the level of weight gain increases from undergainers to overgainers.

CONCLUSION

The combination of pregravid BMI and weight gain pattern is an important determinant of cesarean section rates at term.

Neonatal respiratory morbidity in late-preterm births in pregnancies with and without gestational diabetes mellitus

OBJECTIVE

To evaluate neonatal respiratory morbidity in infants born late-preterm to mothers with or without gestational diabetes mellitus (GDM).

METHODS

Analysis of a population-based cohort of all live-born singletons, born at 34 0/7 to 36 6/7 weeks to mothers with and without GDM, focusing on transient tachypnea of the newborn (TTN) and respiratory distress syndrome (RDS).

RESULTS

The study group comprised 363 (4.7%) singletons born to mothers with GDM and the controls were 7400 born to mothers without GDM. Mothers with GDM were older (31.4 ± 5.1 versus 29.5 ± 5.1 years, p < 0.001) and were more likely to be hypertensive (OR 1.5, 95% CI 1.1-2.1). Neonates of GDM mothers were heavier at birth (2769 ± 539 versus 2636 ± 473 g, p < 0.001). We found a similar incidence of RDS and TTN in both groups. The multiple regression analysis showed cesarean delivery and lower gestational age were independently associated with RDS and TTN.

CONCLUSION

GDM, per se, is not a major contributor to RDS in late pre-term infants. Rather, the combination of prematurity and cesarean birth act independently to increase the risk of respiratory morbidity.

Variations in Multiple Birth Rates and Impact on Perinatal Outcomes in Europe

OBJECTIVE

Infants from multiple pregnancies have higher rates of preterm birth, stillbirth and neonatal death and differences in multiple birth rates (MBR) exist between countries. We aimed to describe differences in MBR in Europe and to investigate the impact of these differences on adverse perinatal outcomes at a population level.

METHODS

We used national aggregate birth data on multiple pregnancies, maternal age, gestational age (GA), stillbirth and neonatal death collected in the Euro-Peristat project (29 countries in 2010, N = 5 074 643 births). We also used European Society of Human Reproduction and Embryology (ESHRE) data on assisted conception and single embryo transfer (SET). The impact of MBR on outcomes was studied using meta-analysis techniques with random-effects models to derive pooled risk ratios (pRR) overall and for four groups of country defined by their MBR. We computed population attributable risks (PAR) for these groups.

RESULTS

In 2010, the average MBR was 16.8 per 1000 women giving birth, ranging from 9.1 (Romania) to 26.5 (Cyprus). Compared to singletons, multiples had a nine-fold increased risk (pRR 9.4, 95% Cl 9.1-9.8) of preterm birth (<37 weeks GA), an almost 12-fold increased risk (pRR 11.7, 95% CI 11.0-12.4) of very preterm birth (<32 weeks GA). Pooled RR were 2.4 (95% Cl 1.5-3.6) for fetal mortality at or after 28 weeks GA and 7.0 (95% Cl 6.1-8.0) for neonatal mortality. PAR of neonatal death and very preterm birth were higher in countries with high MBR compared to low MBR (17.1% (95% CI 13.8-20.2) versus 9.8% (95% Cl 9.6-11.0) for neonatal death and 29.6% (96% CI 28.5-30.6) versus 17.5% (95% CI 15.7-18.3) for very preterm births, respectively).

CONCLUSIONS

Wide variations in MBR and their impact on population outcomes imply that efforts by countries to reduce MBR could improve perinatal outcomes, enabling better long-term child health.

The Quality of Life in Pregnant Women Conceiving Through in Vitro Fertilization

Objective

The aim was to determine whether pregnant women conceiving through in vitro fertilization (IVF) differ from those conceiving spontaneously in terms of psychological well-being and the quality of life.

Methods

In a prospective study we included 75 women conceived after IVF and 78 who conceived spontaneously in the same time period (control group). All the women were sent a self-report questionnaire about demographic and reproductive history, health, pregnancy concerns, containing Subjective Quality of Life Scale (QLS), Positive and Negative Affect Schedule (PANAS), the Psychological Well-Being Scale (PWB), Beck Depression Inventory (BDI), and Zung Self-Assessment Anxiety Scale (SAS); obstetric and newborn’s data were obtained from medical records. Response rate was 66.6% in the IVF and 83.3% in control group.

Results

The mean women’s age was 33.8 years in the IVF, and 32.5 years in the control group (NS). There were no significant differences between groups on the most of the outcome measures assessing psychological status. IVF mothers were just less satisfied in “friend/acquaintances” (P=0.03), a higher percentage had sexual problems prior to conception (P=0.03); the length of hospitalization during pregnancy was longer (P=0.02), and the preterm delivery rate was higher (P=0.01). Withingroup changes over gestation time indicated that IVF women, not controls, showed an increase in positive affect (P=0.04) and purpose in life (P=0.05).

Conclusions

IVF women are inclined to social isolation. Despite more medical problems during pregnancy, they reported improved positive emotions and purpose in life as the pregnancy progressed.

Timing of elective cesarean section and neonatal morbidity: a population-based study

PURPOSE

To assess the incidence of neonatal complications related to gestational age at elective cesarean section near term.

METHODS

We used a population-based dataset to compare neonatal outcomes by gestational age in uncomplicated singleton pregnancies delivered by elective cesarean section ≥37 weeks.

RESULTS

A total of 7364 mothers had an elective cesarean during 2002-2012; 343 (4.7%) at 37, 21 753 (3.8%) at 38, 3140 (2.6%) at 39, 1718 (23.3%) at 40 and 410 (5.6%) at ≥41 weeks. Infants born at a lower gestational age had a higher rate of Apgar scores <7 (2%, 0.4%, 0.6%, 0,3%, 0.2% at 37, 38, 39, 40 and ≥41 week, p = 0.013), hypoglycemia (1.5%, 1.0%, 0.8%, 0.4%, 0.5% at 37, 38, 39, 40 and ≥ 41 week, p = 0.012), hyperbilirubinemia (12.2%, 9.5%, 6.4%, 4.8%, 4.1% at 37, 38, 39, 40 and ≥ 41 week, p < 0.001), respiratory distress syndrome (5.5%, 2.2%, 1.6%, 0.5%, 0.7% at 37, 38, 39, 40 and ≥ 41 week, p < 0.001), and neonatal intensive care admissions (8.7%, 2.3%, 1.9%, 1.0%, 1.7% at 37, 38, 39, 40 and ≥ 41 week, p < 0.001).

CONCLUSIONS

Elective cesarean section at ≥ 39 weeks gestation would significantly reduce neonatal complications.