Prolactin levels during labor.

To test the hypothesis that prolactin (PRL) plays a role in the hormonal events of labor, serum PRL levels in 15 normal secundigravidas were measured on 2 occasions 10-15 days before delivery, at the onset of labor, at cervical dilatation of 5 and 10 cm, at the time of delivery, and on the first, second, and fifth days postpartum. The mean level of PRL was 163 ng/ml +/- 26 ng/ml at the onset of cervical dilatation; it typically decreased with the progress of labor, reaching a value of 140 ng/ml +/- 21 ng/ml at the time of delivery. The differences during the various stages of labor, however, were not found to be statistically significant. Postpartum values were significantly lower (P less than 0.01) on the fifth day after parturition. It is therefore unlikely that PRL is involved in or influenced by the hormonal interplay that occurs during labor.