Another study performed just prior to active labor, in term pregnancies, demonstrated no differences in UA PI, but statistically significant lower values for the middle cerebral artery (MCA) PI, MCA peak systolic velocity (PSV) and normalized umbilical venous blood flow (Q uv) in male compared with female fetuses, but these differences did not translate into differences in perinatal outcome. However, these studies do not take into account possible sex differences.ĭoppler ultrasonographic studies exploring fetal sex differences in the ductus venosus during the first trimester have shown antagonistic results. Longitudinal reference ranges for UA Doppler indices calculated from both cross-sectional and serial measurements have previously been published. The increased UA PI is a marker of raised placental vascular impedance associated with microvascular lesions and correspondingly reduced placental function. Their use in high-risk pregnancies has the potential to reduce obstetric interventions and perinatal deaths. Umbilical artery (UA) Doppler indices, i.e., pulsatility index (PI), resistance index (RI), and systolic/diastolic ratio (S/D) calculated from blood flow velocities, are used as an important clinical tool for evaluating fetal wellbeing in high-risk pregnancies and to predict outcome of growth restricted fetuses.

When using two-dimensional ultrasonography to assess fetal growth, these sex-specific growth charts perform better in identifying small for gestational age (SGA) fetuses at increased risk of fetal demise. Īntenatal growth charts show significant differences in biometrics between male and female fetuses. Sexual dimorphism in the regulation and expression of genes, and signaling pathways, generate differences in placental function and intrauterine environment that may lead to sex differences in health status later in life. Both birth weight and placental weight are higher for males compared with females. The human placenta demonstrates sex-related differences at both structural and functional levels. However, the total mortality from conception to birth is greater among female fetuses. This has been referred to as “the male disadvantage” and the female neonatal survival advantage is well recognized. Male sex is an independent risk factor for unfavorable perinatal outcomes including fetal distress during labor, premature birth, adverse neonatal outcome, and early neonatal death. Previous studies have shown sex-specific differences in fetal development regarding growth and adaption to intrauterine environment. The importance of conducting longitudinal studies and analyzing data accounting for biological differences related to sex has been highlighted a decade ago. We have determined gestational age-dependent sex differences in UA Doppler indices and fetal HR during the second half of pregnancy, and correspondingly established new sex-specific reference ranges intended for refining diagnostics and monitoring individual pregnancies. Female fetuses had higher HR from gestational week 26 +0 until term ( P < 0.05). Female fetuses had 2–8% higher values for UA Doppler indices than male fetuses during gestational weeks 20 +0–36 +6 ( P < 0.05), but not later. UA Doppler indices were significantly associated with gestational age ( P < 0.0001) and fetal HR ( P < 0.0001). ResultsĬomplete data from 294 pregnancies (a total of 1261 observations from 152 male and 142 female fetuses) were available for statistical analysis, and sex-specific reference ranges for the UA Doppler indices and fetal HR were established for the last half of pregnancy. Sex-specific reference intervals were calculated for the fetal heart rate (HR), UA PI, resistance index (RI), and systolic/diastolic ratio (S/D) using multilevel modeling. UA Doppler indices were serially obtained at a 4-weekly interval from a free loop of the umbilical cord using color-directed pulsed-wave Doppler ultrasonography. This was a prospective longitudinal study in women with singleton low-risk pregnancies during 19–40 weeks of gestation. Our main objective was to investigate gestational age-associated changes in UA Doppler indices during the second half of pregnancy and compare the values between male and female fetuses. Therefore, we tested whether fetal sex influences the UA Doppler indices during the entire second half of pregnancy and aimed to establish sex-specific reference ranges for UA Doppler indices if needed. Whether this influences the clinically important umbilical artery (UA) waveform remains controversial, although a few cross-sectional studies have shown sex differences in UA pulsatility index (PI). Sexual dimorphism in placental size and function has been described.

Doppler ultrasound pregnancy at home