Human fetal-placental weight ratio in normal singleton near-term pregnancies

To determine the fetal-placental weight ratio in normal near-term singleton pregnancies.

431 consecutive singleton near-term live deliveries following uncomplicated pregnancies were included in a prospective study. Mean maternal age was 28.6 years (range 17-50), mean parity was 2.9 (range 1-16). Mean gestation age at delivery was 39.7 weeks (range 33-42).

Mean newborn weight was 3,382.1 +/- 486.7 g (range 2,180-4,810). Mean placental weight was 613.0 +/- 123.8 g (range 319-1,266). Mean fetal-placental weight ratio was 5.6 +/- 0.96 (range 2.9-10.6) with kurtosis of 3.6 and skewness of 1.05. The ratio did not differ significantly between male (n = 253) and female (n = 176) infants, 5.7 +/- 0.89 and 5.6 +/- 1.04, respectively. There was a progressive increase in the fetal-placental weight ratio with gestational age (r = 0.87): from 5.3 +/- 0.90 at 33-36 weeks to 5.9 +/- 1.06 at the 41st week and 5.7 +/- 0.71 at the 42nd week (p < 0.05) and with birth weight distribution (r = 0.85) from 5.0 +/- 1. 06 in newborns weighing 2,000-2,499 g to 5.9 +/- 0.94 in newborns weighing >4,000 g (p < 0.05). There was a positive relationship between the fetal-placental weight ratio in teenage and elder parturients (r = 0.98): 5.2 +/- 0.98 (age 17-19), 5.7 +/- 0.88 (age 20-29), 5.6 +/- 1.08 (age 30-39), and 5.7 +/- 0.96 (age 41-50) (p < 0.05). The most contributing variable was birth weight.

The fetal-placental weight ratio tends to be low in teenage women, early near-term gestational age, and low fetal weight. There was a progressive increase in the fetal-placental weight ratio with gestational age and with birth weight distribution.