Amniotic fluid in baboon pregnancies with normal versus growth-retarded fetuses.

Amniotic fluid samples from 12 pregnant baboons at 173 to 176 days of gestation were studied. Five fetuses were growth retarded and seven were normally developed. Mean amniotic fluid volumes and composition (osmolality, protein concentration, delta optical density at 450 nm, and amniotic fluid/maternal plasma creatinine ratio) were similar in the two groups. Growth-retarded fetuses had amniotic fluids with a lower mean (+/- SE) pH than their normally developed peers (7.50 +/- 0.083 versus 7.85 +/- 0.084, p = 0.023). Intrauterine growth-retarded fetuses appeared to ingest amniotic fluid at a slower mean rate than normally developed fetuses (609 +/- 50.9 versus 769 +/- 48.6 ml/day, p = 0.05), but the difference disappeared when the estimates were corrected for fetal weight. Whether these data may be extrapolated to human pregnancies is speculative but appears likely in view of the similarities between amniotic fluid volume and composition in normal baboon and human pregnancies.