Oligohydramnios

Women who agreed to participate were given follow-up appointments at about 20, 28, and 36 weeks' gestation in the National Institute for Health Research Cambridge Clinical Research Facility (Cambridge, UK). All research scans after the dating scan were done with a Voluson i system (GE Healthcare, Fairfield CT, USA) by one of a team of six sonographers, all of whom received standard training. All ultrasound examinations followed the same protocols as those used in the clinical service.13 , 14 (link) At the 20 week research appointment, participants were given a novel questionnaire we created to obtain details about their medical history and demographic characteristics.¹¹ (link) The 20 week scan had both routine (review of fetal anatomy and biometric measurements) and research (uterine and umbilical artery Doppler flow velocimetry) elements. Women were informed about routine elements (any concerns about the fetal anatomy and of the fetal measurements at the 20 week scan), but women and clinicians were masked to the research elements (results of the uterine and umbilical Dopplers). At the 28 and 36 week research appointments, umbilical and uterine artery Doppler flow velocimetry were repeated, and ultrasonographic measurement of fetal biparietal diameter, head circumference, abdominal circumference, and femur length were also done using standard techniques. An estimated fetal weight (EFW) percentile was calculated by use of the Hadlock equations and reference standard.15 (link), 16 (link) Uteroplacental Dopplers, biometry, and EFW results from the research ultrasound scans at 28 and 36 weeks were not reported to the participant or the clinician. However, both were informed about incidental findings, specifically previously undiagnosed placenta praevia, severe oligohydramnios (amniotic fluid index <5), a previously undiagnosed fetal abnormality, or non-cephalic presentation at the time of the 36 week scan.
Gestational age was defined on the basis of ultrasonographic estimation at the time of the first scan, as recommended.³ Distributions of all measurements in the research scans were similar to previously reported reference cohorts (appendix). Summary statistics for reproducibility and reliability of research scans (assessed by two sonographers, scanning the same woman twice at the same appointment, each masked to the results of the other's scan) are tabulated for 45 women at 20 weeks' gestation and 44 women at 36 weeks' gestation (appendix). Coefficients of variation were less than 5% for fetal biometry and EFW, and between 5% and 10% for uteroplacental Doppler at both timepoints.
Women were selected for additional, clinically indicated scans in the third trimester of pregnancy as per routine clinical care, using local and national guidelines (eg, the NICE Guidelines on low risk women,³ women with diabetes,¹⁷ and women with hypertensive disorders¹⁸ ). Women were also screened with serial measurement of the symphyseal-fundal height. All women carried their maternity notes, which included a chart of the normal range of measurements for fetuses in relation to gestational age. Referral for an ultrasound scan was made by the midwife or doctor providing clinical care. Results of all clinically indicated scans were reported and paper copies were filed in both the participant's hand-held notes and hospital case records.
Screening status in relation to EFW was classified on the basis of the last scan before birth (which could be the 28 week scan or the 36 week scan for universal ultrasonography, depending on the gestational age at delivery). Screen positive was defined as an EFW less than the 10th percentile, using an externally derived reference range15 (link), 16 (link) (for both selective and universal ultrasonography). Screen negative was defined as an EFW of the 10th percentile or more (both selective and universal ultrasonography), or if no clinically indicated scan had been done at gestational age of 26 weeks or later (only selective ultrasonography).

All women were grouped according to three bases: age, parity, and a mixture of age and parity. According to age, pregnant women were divided into five groups: the first appropriate age group (20–24 years, A1 group), the second appropriate age group (25–29 years, A2 group), the third appropriate age group (30–34 years, A3 group), the advanced maternal age group (35–39 years old, AMA group), and the very advanced maternal age group (≥40 years, vAMA group). For parity, pregnant women were divided into two groups: a nulliparous group (parity = 1) and a multiparous group (parity ≥ 2). With regard to the mixture of age and parity, pregnant women were divided into 10 groups, combining the two previous groupings. Education was categorized into bachelor’s degree or above and no bachelor’s degree. Residence was divided into urban and rural areas. Marital status was divided into married and unmarried. Smoking was divided into Yes and No. Pre-pregnancy BMI was calculated by dividing pre-pregnancy weight (kg) by the square of height (m²). BMI was divided into four categories using Asian-specific cut-offs (17 (link)): <18.5, 18.5–23, 23–27.5, and ≥27.5 kg/m². Gestational weight gain (GWG) was classified following the 2009 Institute of Medicine (IOM) guidelines, the standard divides GWG into Inadequate, Adequate, and Excessive according to different prenatal weight standards for pregnant women (18 ). Pregnancy was divided into two categories: assisted reproduction and natural conception. Gestational weeks were separated into three categories: 28–31, 32–36, and 37 weeks and above, with deliveries at less than 37 weeks being considered as preterm births. For multiparas, the form of the previous birth was classified into cesarean section and vaginal delivery.
The outcome indicators were maternal pregnancy outcomes and neonatal outcomes. Maternal pregnancy outcomes included gestational hypertension, eclampsia/pre-eclampsia, gestational diabetes mellitus (GDM), intrahepatic cholestasis of pregnancy (ICP), anemia, placenta previa, placental abruption, placental implantation, premature rupture of membranes, postpartum hemorrhage, oligohydramnios, preterm birth, and cesarean section. Neonatal outcomes included macrosomia, fetal distress, transfer to the neonatal unit, neonatal jaundice, and an Apgar score <7 within 5 min of birth. All outcome indicators were diagnosed according to the International Classification of Diseases 10th edition (ICD-10).

Maternal baseline information was derived from the electronic database of the hospitals, including sociodemographic characteristics and reproductive history. We further abstracted the ART procedures and most of the perinatal outcomes from the database of the hospitals, while the neonatal morbidity and mortality were followed up and recorded by well-trained clinical personnel. The pregnancy outcomes assessed included hypertensive disorders in pregnancy (HDP), GDM, Intrahepatic cholestasis of pregnancy (ICP), placental abruption, placenta previa, oligohydramnios, premature rupture of membrane (PROM), postpartum hemorrhage (PPH) and mode of delivery. While neonatal outcomes were assessed including the gender of neonates, birth weight, preterm birth (PTB), weight for gestational age, neonatal infection, admission to the neonatal intensive care unit (NICU), neonatal asphyxia, neonatal jaundice, and congenital anomaly. Preterm birth was defined as delivery at less than 37 weeks, and very preterm was defined as delivery of baby between 28 and 32 gestational weeks of pregnancy. LGA or SGA was defined as a birth weight more than 90th centile or less than 10th centile of our population for a specific gestational age and sex, respectively (19 (link), 20 (link)). Diagnoses were coded according to the International Classification of Diseases version 10(ICD-10).

All demographic data regarding FET cycles were collected from our fertility center’s EMRs. The obstetric and neonatal complications were obtained from the EMR system in the Department of Obstetrics of our hospital. Live birth was defined as a fetus born alive after 28 weeks of pregnancy. The primary aim was to examine obstetric outcomes, specifically the incidence of gestational hypertension. The four categories of HDP were preeclampsia, gestational hypertension, superimposed preeclampsia, and chronic hypertension. Gestational hypertension was defined as hypertension after 20 weeks of gestational age without proteinuria. Additional obstetric outcomes that were examined included gestational diabetes, premature rupture of membranes (PROM, beyond 37 weeks of gestation and prior to the onset of labor), preterm premature rupture of membranes (PPROM, rupture of membranes prior to 37 weeks of gestation), placenta previa, placenta accreta, abnormal umbilical cord, polyhydramnios, oligohydramnios, postpartum hemorrhage (estimated blood loss ≥ 500 mL in a vaginal delivery or ≥ 1000 mL in a cesarean delivery), and cesarean delivery. The spectrum of abnormal umbilical cord includes the following types: presentation of umbilical cord, torsion of cord, excessively long cord, true knot, and abnormal insertion (e.g., vasa previa, battledore placenta, and velamentous insertion).