Maternal and fetal factors related to abnormal amniotic fluid

The objective of this study was to identify maternal and infant characteristics related to alteration of amniotic fluid volume at birth.

A series of 27,145 consecutive malformed newborn infants from the Spanish Collaborative Study of Congenital Malformations (ECEMC) was analyzed. From this total, 3.01% were found to have oligohydramnios and 3.69% were found to have polyhydramnios.

As expected, renal/urinary tract and lung defects were associated with oligohydramnios, whereas esophageal and intestinal atresias, neural tube defects, and other central nervous system malformations were associated with polyhydramnios. In addition, other defects such as cardiovascular anomalies, hydrocephaly, and microcephaly were also related to abnormalities of amniotic fluid volume. After excluding the defects whose association to oligo- or polyhydramnios is well recognized, we compared the frequency of different variables among them and with infants with a normal volume of amniotic fluid. In comparison with infants with normal amniotic fluid volume, the groups with oligo- and polyhydramnios had lower birth weight, shorter gestational age and umbilical cord, higher parental ages, and a greater frequency of spontaneous abortions. The differences were more marked for weight in newborn infants with oligohydramnios, and for gestational age, umbilical cord length, number of previous pregnancies, and spontaneous abortions in polyhydramnios cases. Placental weight was lower in oligohydramnios cases than in infants with normal amniotic fluid, and higher in polyhydramnios cases. Parental consanguinity and twinning were more frequent in polyhydramnios. Maternal morbidity was higher in both groups with abnormal amniotic fluid volume, especially for acute diseases such as hypertension, diabetes mellitus, and gestational diabetes. Chromosomal aberrations were more frequent in the oligo- and polyhydramnios groups than in cases with a normal volume of amniotic fluid, which supports the suggestion of performing prenatal cytogenetic analysis in any pregnancy complicated by an abnormal volume of amniotic fluid.

The fact that all of these results are similar in the control group of healthy infants suggests that at least some of the variables associated with abnormal amniotic volume could be considered as causal factors altering the production of fluid.