Ultrasound in first trimester shows no difference in fetal size between the sexes

Sex Differences in Nutrition, Growth, and Metabolism in Preterm Infants

Biological differences between the sexes are apparent even from the early part of the pregnancy. The crown-rump length is larger in male fetuses compared to females in the first trimester. Placentae of male and female fetuses have different protein and gene expressions, especially in adverse conditions. Even within the intrauterine milieu, the same extracellular micro RNA may show upregulation in females and downregulation in male fetuses. There appears to be a natural survival advantage for females. Maternal glucocorticoids (GC) play an important role in fetal growth and organ maturation. However, excess glucocorticoids can not only affect growth but the response may be sex-specific and probably mediated through glucocorticoid receptors (GR) in the placenta. Mild pre-eclampsia and asthma are associated with normal growth pattern in males, but in female fetuses, they are associated with a slowing of growth rate without causing IUGR probably as an adaptive response for future adverse events. Thus, female fetuses survive while male fetuses exhibit IUGR, preterm delivery and even death in the face of another adverse event. It is thought that the maternal diet may not influence growth but may influence the programming for adult disease. There is growing evidence that maternal pre-pregnancy overweight or obesity status is directly associated with a higher risk of obesity in a male child, but not in a female child, at 1 year of age. It is observed that exposure to gestational diabetes is a risk factor for childhood overweight in boys but not in girls. It is fascinating that male and female fetuses respond differently to the same intrauterine environment, and this suggests a fundamental biological variation most likely at the cellular and molecular level.

Sex-related growth differences are present but not enhanced in in vitro fertilization pregnancies

OBJECTIVE

To determine whether IVF modifies the effect of fetal sex on growth.

DESIGN

Retrospective cohort study.

SETTING

Tertiary care center and related facilities.

PATIENT(S)

Singleton live births without fetal/maternal comorbidities from fertile women who conceived without the use of assisted reproductive technologies and infertile women who conceived with IVF.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The primary outcome was birth weight (BW). Secondary outcomes were fetal crown-rump length (CRL) in the first trimester, biparietal diameter (BPD), and estimated fetal weight (EFW) in the second trimester.

RESULT(S)

There were no differences in baseline characteristics between women carrying male fetuses and those carrying female fetuses in either mode of conception. In unadjusted analyses, the male-female differentials in fetal BPD and BW were more pronounced in the IVF cohort than in the unassisted cohort. In multivariable regression analysis, male BPD exceeded female BPD by 0.12 cm, male EFW exceeded female EFW by 12 g, and male BW exceeded female BW by 172 g. IVF did not have a significant effect on BPD but was associated with a 52 g increase in EFW in the midgestation. IVF was associated with an 81-g reduction in BW. IVF did not modify the magnitude of size differences between the sexes in the midgestation or at birth.

CONCLUSION(S)

Comparable sex-dependent differential growth occurs in unassisted and IVF pregnancies.

Fetal transverse cerebellar diameter measured by ultrasound does not differ between genders

PURPOSE

The aim of this study was to determine the correlation between fetal transverse cerebellar diameter (TCD) and gestational age of male and female fetus in women under low-risk prenatal care between the 13th and 40th week of gestation.

METHODS

A cross-sectional study was carried out with 184 pregnant women, at the age of 18 years or more, gestational age ranging from 13 to 40 weeks, with a single fetus. A single TCD measurement by ultrasound was used for each fetus. Correlations between fetal TCD and gestational age were determined for the whole sample and each gender separately.

RESULTS

We identified 102 males and 82 female fetuses. A linear correlation was observed between fetal TCD and gestational age for the whole sample (r = 96.9%; p < 0.001). A significant linear correlation was also observed for both males (r = 97.0%; p < 0.001) and females (r = 96.9%; p < 0.001). Comparing the regression lines between genders, no significant difference was observed.

CONCLUSIONS

The data of this study suggest TCD fetal ultrasound as a predictive biometric parameter of gestational age independently of fetal gender in the last two trimesters of a pregnancy.

Mid-trimester ultrasound prediction of gestational age: advantages and systematic errors

OBJECTIVE

To detect possible sources of bias in ultrasound prediction of gestational age.

SUBJECTS AND METHODS

Using the Swedish Medical Birth Registry, 571 617 women were identified who were delivered between 1990 and 1997 and who had obtainable information on last menstrual period and expected date of delivery according to ultrasound.

RESULTS

Male fetuses were more likely than females to be judged older than the last menstrual period date suggested at early fetometry. The estimated magnitude of the systematic error by infant gender corresponded to 1.5 days. Similarly, the fetuses of young women, multiparous women, smokers and women with low educational level were at increased risk of being smaller than expected at ultrasound examination in early pregnancy. A strong association was seen between adjustments of expected date of delivery -7 days or more and small-for-gestational age according to ultrasound at birth. Compared to singleton pregnancies, twin pregnancies were more likely to be judged more progressed at ultrasound fetometry than the last menstrual period date suggested.

CONCLUSIONS

Compared to last menstrual period estimates, routine ultrasound measurements to predict date of delivery are comparatively reliable but systematic errors are inherent in the method. The erroneous adjusted dates may be due to incorrect measurements or systematic bias (e.g. gender), but they are also likely to reflect early growth restriction (e.g. in the case of maternal smoking and small-for-gestational age). Further studies are needed to investigate whether the systematic errors in ultrasound prediction of gestational age could lead to suboptimal obstetric management in adjusted pregnancies.

Sex difference in fetal head growth

Growth of the fetal biparietal diameter (BPD) throughout the second and third trimesters was measured in a prospective longitudinal study. Linear-cubic equations were fitted to the data of individual fetuses and from these equations mean growth curves were produced for males and females. The head growth trajectories of males and females were significantly different. The study illustrates why the practice of dating pregnancies by ultrasonic fetal BPD measurement at about 16 weeks gestation can lead to error.