Effects of fetal sex and race on risk of very preterm birth in twins

Optimal threshold for birth weight discordance: Does knowledge of chorionicity matter?

OBJECTIVE

To establish the optimal threshold of birth weight discordance (BWD) for prediction of stillbirth, perinatal mortality and morbidity in twins born in British Columbia with or without chorionicity information.

STUDY DESIGN

This is a retrospective population-based cohort study of twins born in British Columbia from 2000 to 2010. Data from one hospital was used to adjust for chorionicity. Multivariate generalized estimating equation and receiver operating characteristic curve analyses were performed to evaluate the predictability of BWD in comparison with other fetal anthropometric measurements. Positive likelihood ratio is used to estimate test accuracy. Survival analysis was conducted to take gestational age and other confounders into account.

RESULTS

We analyzed two cohorts, with (pairs=1493) and without (pairs=6328) chorionicity information, of which 1.5% experienced stillbirth, 2.9% suffered perinatal mortality and 22.6% identified with perinatal morbidities. BWD was a significant predictor of stillbirth. Standard receiver operating characteristic curve analysis and survival analysis suggested that BWD of ⩾30% is the optimal thresholds for stillbirth and perinatal mortality irrespective of chorionicity. However, the P-value for predictive accuracy of BWD was nonsignificant for perinatal morbidity, after adjusting for confounding variables engaging multivariate analysis. Sex discordance can be used as a proxy for chorionicity.

CONCLUSION

BWD is a good predictor for stillbirth. A BWD cutoff limit of 30% and higher has optimal accuracy for detecting perinatal mortality.

Relationship of mode of conception and sex concordance with mortality/morbidity in preterm twins

OBJECTIVE

To assess the association of mode of conception and sex concordance with neonatal outcomes in very preterm twins.

STUDY DESIGN

Twin pairs born at gestational age ≤ 32 weeks and admitted to a Level 3 neonatal intensive care unit (NICU) in 2010-2011 were retrospectively identified from the Canadian Neonatal Network™ database. A composite outcome representing neonatal mortality or any severe morbidity (intraventricular hemorrhage grades ≥ 3 or periventricular leukomalacia, retinopathy of prematurity stages ≥ 3, bronchopulmonary dysplasia, or necrotizing enterocolitis stages ≥ 2) was compared between twins conceived using assisted reproduction technologies (ARTs) or spontaneously (SP), and tested for association with sex concordance in individual-level and pair-wise multivariable logistic regression analyses.

RESULTS

Study subjects included 1,508 twins from 216 ART (53 [25%] male-male, 104 [48%] male-female, and 59 [27%] female-female) and 538 SP (192 [36%] male-male, 123 [23%] male-female, and 223 [41%] female-female) pairs. No statistically significant association was detected between mode of conception and the composite outcome of mortality/morbidities. The composite outcome was significantly higher in same-sex than in opposite-sex twins (OR = 1.68; 95% CI = [1.09, 2.59]). This relationship was most pronounced in ART pairs (OR = 2.25; 95% CI = [1.02, 4.98]), with increased rates in one or both twins from male-male versus opposite-sex ART pairs (OR = 3.0; 95% CI = [1.07, 8.36]).

CONCLUSION

Same-sex pairing was associated with higher mortality/morbidities in very preterm twins admitted to the NICU, and can be used in clinical practice to identify twins at higher risk of adverse neonatal outcomes.

Effects of perinatal testosterone on infant health, mother-infant interactions, and infant development

OBJECTIVE

Many researchers and health care providers have noticed male vulnerability in infant health, mother-infant interactions, and some infant cognitive development, especially among very low birth weight (VLBW) preterm infants. However, factors beyond gender that could explain these observed differences have not been clear. The purpose of this article is to review the literature on the subject and to introduce a conceptual framework relating these factors.

DISCUSSION

According to gender-difference theories, prenatal exposure to high levels of testosterone may influence infant health and mother-infant interactions by negatively affecting infant cognitive/motor/language development. We constructed a conceptual framework based on the associations among biological (perinatal testosterone), stress-related (perinatal and maternal cortisol), and developmental (infant cognitive/motor/language skills) factors. If research establishes these biological, environmental, and developmental associations in mother-VLBW preterm pairs, the results will highlight the importance of addressing gender differences in nursing research and encourage the development of nursing interventions designed to reduce stress among mothers of VLBW preterm infants, particularly male infants.

CONCLUSION

From a psychobiosocial perspective, combining biophysiological factors such as perinatal testosterone and cortisol with socioenvironmental factors such as the quality of mother-infant interactions and infant temperament may provide a broader view of gender differences in infant health and development.

Contribution of twin-to-twin transfusion syndrome to preterm birth among monochorionic biamniotic and bichorionic biamniotic twin pregnancies

AIMS

To determine the contribution of twin-to-twin transfusion syndrome (TTTS) to preterm birth (PTB) at <37 weeks of gestation among Japanese twin pregnancies.

METHODS

An observational study using 3241 MC-BA (monochorionic biamniotic) and 6581 BC (bichorionic biamniotic) twin pregnancies. We focused on TTTS, preterm premature rupture of membranes (PPROM), pregnancy-induced hypertension (PIH), and fetal sex as possible causes of PTB.

RESULTS

PTB was more common in MC-BA than in BC twin pregnancies (66.9% vs. 57.6%, P<0.0001) whereas PTB after PPROM (8.0% vs. 10.0%) and PIH (5.7% vs. 5.9%) was not. PTB after TTTS occurred in 7.3% of women with MC-BA twins. PTB was significantly more common for male-male pairs than for female-female pairs among both MC-BA (69.2% vs. 64.7%) and BC (59.6% vs. 56.3%) twins.

CONCLUSION

The elevated risk of PTB among MC-BA twins could be explained by the occurrence of TTTS.

Does fetal sex influence the risk of preterm delivery in dichorionic twin pregnancies after spontaneous conception?

OBJECTIVE

The incidence of preterm delivery has been increasing, and our aim was to estimate the influence of fetal sex on the risk of preterm delivery in dichorionic twins after spontaneous conception.

METHODS

125 spontaneously conceived dichorionic twin gestations, with viable fetuses, born after 24 weeks and delivered spontaneously before 37 weeks, were enrolled. The impact of fetal sex, previous preterm delivery, maternal age, body-mass-index, smoking, and parity on gestational age at birth were evaluated.

RESULTS

Despite similar baseline characteristics in all three groups, women with one or two male fetuses delivered significantly more often before 34 weeks than patients with two female fetuses, 48% (23/48) and 43% (19/44) vs 21% (7/33), p = .04. Regression analyses, including fetal sex, maternal age, maternal body-mass-index, smoking, previous preterm delivery and parity, revealed that only fetal sex was significantly associated with spontaneous preterm delivery (p = .03).

CONCLUSION

Fetal sex appears to be a risk factor for preterm delivery in spontaneously conceived dichorionic twin gestations. Twin pregnancies with one or two male fetuses seem to be at higher risk for spontaneous preterm delivery than those with only females.

Effects of gender on the health and development of medically at-risk infants

OBJECTIVES

To examine gender-differentiated health and cognitive/motor/language developmental outcomes among medically at-risk infants.

DESIGN

Longitudinal descriptive and comparative secondary analysis.

SETTING

Neonatal Intensive Care Unit, intermediate care unit, and infectious disease clinic of tertiary medical centers in the southeast and east United States.

PARTICIPANTS

One hundred eight (108) premature infants, 67 medically fragile infants, and 83 infants seropositive for HIV.

METHODS

Neonatal and later health variables were obtained from the medical record to determine the technology dependence scores and frequency of common health problems. Data for physical growth and cognitive/motor/language development were obtained through the physical measurement, including the Bayley Scales of Infant Development-Second Edition, the Vineland Adaptive Behavior Scale, the Toll Control Developmental Checklist, and the Preschool Language Scale-3 during home visits between 6 and 27 months corrected ages.

RESULTS

Fewer effects on health and developmental outcomes related to gender were observed with medically fragile infants than the other two groups of infants. The cognitive/motor/language scores were decreased with increasing age of the infants in all groups.

CONCLUSION

Male gender can be considered a significant biological risk factor for infants' cognitive and motor development, especially for premature infants. Because of their increased risk, it is recommended that male infants who are born prematurely or seropositive for HIV have early and advanced developmental screening tests by trained personnel through periodic pediatric clinic.

The impact of fetal gender on prematurity in dichorionic twin gestations after in vitro fertilization

BACKGROUND

Impact of fetal gender on prematurity has been primarily investigated in singleton pregnancies. In an attempt to understand better how fetal gender may affect gestational length in twin gestations after in vitro fertilization, same-sex twins and opposite twins were compared for pregnancy duration.

METHODS

This study evaluated 113 women at ages 20 to 39 years with consecutive dichorionic-diamniotic twin gestations after assisted reproduction. All pregnancies were results of fresh in vitro fertilization (IVF) cycles with use of autologous oocytes and sperm and were delivered at up to 37 weeks of gestation at a University-based high-risk, maternal-fetal medicine unit.

RESULTS

Both groups did not differ in baseline characteristics, such as maternal ages, indications for fertility treatments, number of previous IVF attempts, body mass index and parity. Opposite sex- twins, however, presented with significantly shorter gestational age at birth (32.9 +/- 3.4 weeks) than same-sex twins (34.3 +/- 2.5 weeks), (p < 0.05). Younger maternal age was also associated with shorter pregnancy duration (p < 0.05).

CONCLUSIONS

Fetal gender mix serves as risk factor for more significant prematurity in dichorionic-diamniotic twins after assisted reproduction with opposite sex twins at higher risk than same sex-twins.

The contribution of maternal race/ethnicity and fetal sex to prematurity in twins

OBJECTIVE

The contribution of male fetal sex to twin preterm birth (PTB) rates was evaluated in the United States.

STUDY DESIGN

The 2002 National Center for Health Statistics Natality database was analyzed for fetal sex and twin gestations based on birth sex for MM and FF pairs (M, male; F, female). Multivariable Cox proportional hazards regression was applied to estimate the hazard ratio for PTB with adjustments for known risks.

RESULTS

Thirty-three thousand nine hundred twenty-six pairs were analyzed. PTBs between 20-36 completed weeks occurred in 59.1% MM pairs and 57.5% FF pairs. MM sex was an independent risk factor for PTB. This effect was greatest for deliveries between 20-29 weeks (hazard ratio, 1.224; 95% CI, 1.113-1.346). The effect was most pronounced in non-Hispanic white MM pairs.

CONCLUSION

In the United States, MM pairs are at greater risk for PTB. Race and ethnicity modulate sex effects. Further studies are needed to understand potential mechanisms.

Sex ratio is remarkably constant

OBJECTIVE

To study whether the sex of the offspring is related to increasing parental age, gravidity, and parity, hypothesizing an altered male-to-female sex ratio with the advancing parental age.

DESIGN

A large retrospective cohort study.

SETTING

The study analyzed birth records of Hadassah Hebrew University Medical Center in Jerusalem from June 2003 to December 2006.

PATIENT(S)

35,837 birth records were analyzed including 941 multifetal deliveries, excluding foreign inhabitants (n = 744), missing data for the main study outcome (n = 2) and parturients over 50 years to control for egg donation (n = 26).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Male-to-female sex ratio.

RESULT(S)

The male-to-female sex ratio of all the newborns was 1.05. This ratio did not change significantly with either maternal or paternal age. Neither gravidity nor parity affected the male-to-female ratio. The only factor that affected the regression of sex ratio was the length of gestation.

CONCLUSION(S)

Sex ratio at birth is remarkably constant. No association was found between parental age or birth order and neonatal sex ratio.

Male sex and intraventricular hemorrhage

BACKGROUND

Neonatal mortality and morbidity are sex biased in low birth weight infants. The "Y chromosome effect" has been suggested to be responsible for these maturational differences.

OBJECTIVE

To examine the association of sex and neonatal outcomes.

DESIGN AND METHODS

A retrospective observational study. Data on all low birth weight infants who survived for >48 hrs were analyzed. Neonatal outcomes were compared between male and female infants. A regression model was used to detect the influence of sex on outcomes after controlling for confounders. Analysis was repeated after stratification of infants into three groups: group A (<1000 g), group B (1000-1499 g), and group C (1500-2499 g).

RESULTS

A total of 833 infants were included in this study; 419 female infants and 414 male infants. Male infants had an increased rate of overall intraventricular hemorrhage (IVH) (12.2% vs. 7.2%, p = .02) and IVH grades 3-4 (4.8% vs. 2.3%, p = .04). In addition, male infants had higher bilirubin levels (10.19 +/- 3.1 mg/dL vs. 9.32 +/- 2.94 mg/dL, p = .001). In a regression model, male sex continued to have significant influence on IVH, IVH grades 3-4, death, and bilirubin. In group A, male infants had a significantly increased prevalence of death (regression coefficient, 1.82 +/- 0.65; p = .005) that could not be explained by the increased prevalence of IVH (p = .18) in regression analysis. In group B, male sex was significantly associated with a higher bilirubin level (regression coefficient, 0.94 + 0.3; p = .002). In bivariate analyses, IVH and IVH grades 3-4 were significantly higher in male compared with female infants (19.8% vs. 3.9%, p < .0001) and (8.5% vs. 0.97%, p = .02), respectively, but these differences lost significance in multiple-regression analysis. In group C, male sex positively influenced the prevalence of IVH (regression coefficient, 1.7 +/- 0.57; p = .003). Bilirubin measured higher in male infants (11.38 +/- 2.87 mg/dL vs. 10.19 +/- 3.22 mg/dL, p = .0004), but the difference lost significance in regression analysis (regression coefficient, 0.21 +/- 0.31; p = .5).

CONCLUSIONS

Bilirubin, IVH, and death were significantly higher in male infants. In subgroup analysis, significance was retained in group A (<1000 g). Whether a single biological factor is responsible for these differences or perhaps a multi-causal process involving a complex interaction of physiologic, environmental, and pathologic responses needs to be further addressed in future research.

Gender mix in twins and fetal growth, length of gestation and adult cancer risk

This study evaluated the effect of gender mix (the gender combinations of twin pairs) on fetal growth and length of gestation, and reviewed the literature on the long-term effects of this altered fetal milieu on cancer risk. In singletons, it is well established that females weigh less than males at all gestations, averaging 125-135 g less at full term. This gender difference is generally believed to be the result of the effect of androgens on fetal growth. The gender difference in fetal growth is greater before the third trimester and less towards term, with males growing not only more, but also earlier than females. Plurality is a known risk factor for reduced fetal growth and birthweight. Compared with singletons, the mean birthweight percentiles of twins fall substantially (by 10% or more) below the singleton 10th percentile by 28 weeks, below the singleton 50th percentile by 30 weeks, and below the singleton 90th percentile by 34 weeks. In unlike-gender twin pairs, it has been reported that the female prolongs gestation for her brother, resulting in a higher birthweight for the male twin than that of like-gender male twins. Other researchers have demonstrated that females in unlike-gender pairs had higher birthweights than females in like-gender pairs. Analyses from our consortium on 2491 twin pregnancies with known chorionicity showed longer gestations and faster rates of fetal growth in both males and females in unlike-gender pairs compared with like-gender male or female pairs, although these differences were not statistically significant. The post-natal effects for females growing in an androgenic-anabolic environment include increased sensation-seeking behaviour and aggression, lowered visual acuity, more masculine attitudes and masculinising effects of the auditory system and craniofacial growth. In contrast, there is no evidence to suggest that there might be a similar feminising effect on males from unlike-gender pairs. This hormonal exposure in utero may influence adult body size and susceptability to breast cancer.

The Association Between Fetal Sex and Preterm Birth in Twin Pregnancies

OBJECTIVE

To assess the association between the fetal sex and preterm birth.

METHODS

We performed a retrospective population-based cohort study using the 1995-1997 registration twin data in the United States (148,234 live-birth twin pairs). The twin pairs were divided into 3 groups: male-male (male-male), female-female, and opposite sex. We used 3 different cutoff values of preterm birth: less than 28, 32, and 36 gestational weeks. The preterm birth rates among the 3 study groups were compared, and the adjusted risk ratios (relative risk) were estimated by multiple logistic regression.

RESULTS

The male-male twin pairs had the highest pre-term birth rate (less than 28 weeks: 4.9%; less than 32 weeks: 12.4%; less than 36 weeks: 40.2%), the female-female twin pairs were intermediate (less than 28 weeks: 4.1%; less than 32 weeks: 10.6%; less than 36 weeks: 37.8%), and the opposite-sex twin pairs had the lowest rate (less than 28 weeks: 4.1%; less than 32 weeks: 10.1%; less than 36 weeks: 36.8%). Adjustment for important confounding factors or excluding twin pairs born to mothers who had an induction of labor or a cesarean delivery with medical complications did not change the results. The adjusted relative risks (95% confidence intervals) were 1.19 (1.11, 1.27), 1.21 (1.16, 1.26), and 1.09 (1.07, 1.11), respectively, for male-male twins compared with the opposite-sex twins under the 3 different cutoff values of preterm births.

CONCLUSION

Male sex is associated with increased risk of preterm births in twin pregnancy.

LEVEL OF EVIDENCE

II-2

A comparison of risk factors for twin preterm birth in the United States between 1981-82 and 1996-97

OBJECTIVE

This paper examines risk factors for twin preterm birth in 1981-82 and 1996-97 in the United States in order to see if they have changed over time.

METHODS

We studied all U.S. twin births for the years examined (N = 346, 567). Since the gestational age distributions for twins differs from singletons, the risk of preterm birth was examined at <33, 33-34, and 35-36 weeks. Logistic regression was used to examine the contributions of sociodemographic and obstetric factors at each period.

RESULTS

While the <33 week twin preterm rate rose 7% from 1981-82 to 1996-97, the 33-34-week rate rose 31%, and the 35-36-week rate rose 51%. Women with less education, teenagers, unmarried women, primiparas, and blacks were more likely to deliver preterm across all three preterm birth levels. However, the effect of these low socioeconomic status markers diminished over the study period. Additionally, the odds of preterm birth among blacks increased with earlier gestational ages. Women who had intensive prenatal care utilization as compared with less than adequate utilization were more likely to deliver preterm (35-36 weeks) in 1996-97 (odds ratio (OR) = 2.05) compared with 1981-82 (OR = 1.44). Smaller increases were noted for <33 and 33-34 weeks.

CONCLUSIONS

Obstetric factors appear to be playing a greater role in the rise of twin preterm births at 35-36 weeks gestation. Temporal sociodemographic changes do not explain the rise in the preterm rate. Changing clinical practices may be having unintended consequences on the public health goals of reducing preterm and low birthweight rates in the United States.

The uterine capacity measured by the total twin birth weight and duration of twin pregnancy

The objective of this study was to answer the question whether there is the relation between the uterine capacity, estimated by the total birth weight of fetuses, and the duration of twin gestation. The material for researches contains data received from the books of births and case records concerning the pregnant who gave births to twins in the Institute of Obstetrics and Gynecology of the Medical University in Lódź between 1970-1998. The final analysis concerned only gestations lasting more than 29 weeks, without any complications (excluding prematurity and the growth-discordant twins), and when gestational age was exactly known. The selected group was finally composed of 188 pairs of twins. The analyses considered relations between total birth weight of twins, the sex of newborn babies, parity, and the duration of gestation. The duration of the analyzed twin pregnancies was 35.6 weeks, including primiparous with 35.8 weeks, and multiparous--35.1 weeks. In the group of male-male twin pairs the average duration of pregnancy was 35.7 weeks, in unlike-sexed pairs--35.6 weeks, and in female-female pairs--35.5. In the group of the primiparous having male-male twin pairs the average duration of pregnancy was 35.1 weeks, unlike-sexed pairs--36.4 weeks and female female pairs--36.6 weeks, while in the group of multiparous relatively: 36.4, 35.4, 35.0 weeks. The total birth weight of the specific pairs of twins was from 2270 g to 6900 g (average 4794 g), while in 92% < 5500 g. In the primiparous group it was 4908.1 g. and in the multiparous group--4663.1 g. Analyzing the total twins' weight according to the fetal gender and parity it was found that in primiparous with male-male twins--4715.3, unlike-sexed--5271.6 and female-female--4967.5, whereas in multiparous relatively: 4961.5, 4692.6, 4414.0. The shortening of twin pregnancies was caused by the following factors: total body mass achieved by fetuses was > 5500 g, presence of male sex in twin pregnancies (only in primiparous), and also the multiparity.

Twin birth weight discordance and risk of preterm birth

OBJECTIVES

Our purpose was to determine whether birth weight discordance is a risk factor for preterm birth of twins, and to further characterize the relationships involved.

STUDY DESIGN

Maternally linked 1978-1990 Missouri birth certificates were used to analyze gestations resulting in live twins. We used contingency tables and multiple logistic regression.

RESULTS

The degree of discordance correlated strongly with risk for live preterm birth but only for discordances >30% and preterm birth at <32 weeks' gestation. Among 9479 pregnancies with discordance <30%, 9.5% ended in birth at <32 weeks' gestation, versus 13.7% of 326 with discordance of 30% to 40% (P =.03) and versus 34.1% of 126 with discordance > or =40% (P <. 001). There were 42 preterm twin births at <32 weeks' gestation with discordances > or =40%. Of these, 51% were attributable to fetal growth restriction and 16% to large size for gestational age in one infant; in 72% the smaller twin was the second born, and in 86% the twins were like sex. The relative association between > or =40% discordance and preterm birth at <32 weeks' gestation was strengthened (final odds ratio, 9.54; P <.0001) in a multivariate model containing other risk factors for delivery at <32 weeks' gestation: black race, either twin small for gestational age, unmarried, teenage mother, number of male fetuses, like fetal sex, education <12 years, nulliparity, and cigarette smoking.

CONCLUSIONS

Twin birth weight discordance has now clearly been demonstrated to be a risk factor for preterm birth. The effect was found particularly with discordances > or =40% before 32 weeks' gestation. Discordance was usually attributable to fetal growth restriction, most often in the second-born twin.

Trajectories of fetal loss in the czech republic

Using data for 555,038 pregnancies conceived in the Czech Republic in 1987-1990, we show that pronounced differences in fetal survival in the middle trimester of pregnancy by marital status, educational level, and labor force attachment become much smaller at full term; survival differences by age at conception and number of previous deliveries show relatively constant proportional hazards throughout gestation. Social inequalities in postpartum life chances have been documented previously, but we show that similar inequalities exist before birth.