Growth of total intrauterine, intra-amniotic and placental volume in normal singleton pregnancy measured by ultrasound.

The growth of total intrauterine, intra-amniotic and placental volume during the latter half of pregnancy was studied longitudinally with ultrasound in 115 healthy women with normal singleton pregnancies. A parallel planimetric area method was used. The range and distribution of normal values between 20 and 40 weeks was determined for a main study group of 103 primiparous women with which values from 12 parous women were compared. Total intrauterine volume increased from a median of 1006 ml to 4420 ml, intra-amniotic volume from 716 ml to 3406 ml and placental volume, calculated as the difference between total intrauterine and intra-amniotic volume, increased from 259 ml to 801 ml. Variation between individuals was wide at all stages of pregnancy. No significant difference was found between primiparous and parous women. Between successive 5-week periods from 20 to 40 weeks there was evidence that women tended to maintain their initial volume ranking. During the 30-35 week period, rate of growth of total intrauterine and intra-amniotic volume was somewhat faster than the near constant mean rate at other times, while the rate of growth of placental volume decreased after 30 weeks towards term.