Characteristics of fetuses with polyhydramnios and abnormal chromosome study

Abstract

It is readily acknowledged that chromosomal abnormalities are associated with polyhydramnios. The purpose of this retrospective study was to identify risk factors for an abnormal chromosome study among cases with polyhydramnios.

MATERIAL AND METHODS: Data was collected at Magee-Womens Hospital (N=169) and Henry Ford Hospital (N=48). A routine obstetrical ultrasound examination was performed on singleton fetuses between 18 and 42 weeks gestation. Standard fetal biometric data and amniotic fluid index were obtained. A detailed fetal anatomic survey was carried out in each case. Polyhydramnios was defined as an AFI of >25.0 cm and was categorized into three groups by severity: mild (AFI: 25.0-30.0 cm); moderate (AFI: 30.1-35.0 cm); and severe (AFI> 35.1 cm). Cases with polyhydramnios secondary to isoimmunization and diabetes were excluded from the study. All patients were offered the option of amniocentesis. Patients were also offered amniocentesis due to age of ≥35 years or if a multiple marker screen indicated a risk of > 1:270 for Down syndrome or a risk for trisomy 18. A weight percentile was calculated for each neonate.

RESULTS: 217 singleton pregnancies had AFI >25.0 cm. 69 patients (32%) underwent amniocentesis. 4 additional newborns underwent chromosome study due to abnormal features undetected by ultrasound. 9 cases in the study group (4.14%) had an abnormal chromosome study. Each of these 9 fetuses had at least one sonographically detectable congenital malformation. The severity of polyhydramnios in these 9 cases was variable. Three neonates in the control group underwent chromosome study because of abnormal phenotypic characteristics. All three were chromosomally normal. After controlling for maternal age, the incidence of karyotypic abnormalities was higher with polyhydramnios than with a normal amount of amniotic fluid. The distribution of neonatal weights for the cases with polyhydramnios was as follows: 14 (6.4%) were small-for-gestational age (SGA); 159 (73.4%) were average-for-gestational age (AGA); and 44 (20.2%) were large-for-gestational age (LGA). 6 of 14 SGA fetuses vs. 2 of 159 AGA fetuses were karyotypically abnormal. Although 5 of 44 (11.4%) LGA fetuses had a sonographically detectable congenital malformation, none were karyotypically abnormal. The incidence of an abnormal karyotype among SGA newborns with polyhydramnios was significantly higher than among AGA and LGA newboms (p < 0.001).

CONCLUSION: Among cases with AFI>25.0-cm, small for gestational age, and fetuses with ultrasonically detected anomalies are at risk for abnormal chromosome study. In the absence of these findings one should not consider amniocentesis.