Birth follows "mysterious" rhythms

Nutrition Health Review, Wntr, 1989

Birth Follows "Mysterious" Rhythms

Like many other bodily functions, labor follows a circadian rhythm, cycling in a 24-hour pattern. According to a team of investigators from the universities of Missouri and Michigan, the normal pattern, with its peak onset between midnight and 2 a.m., also holds true for premature births and for pregnancies complicated by intrauterine growth retardation. But the researchers found that the pattern shifts if the birth is complicated by chorioamnionitis, an inflammation of the placenta and the membrane that surrounds the fetus.

If inflammation -- usually caused by infection -- exists, labor tends to start earlier in the evening. In looking at records of more than 17,000 term and 1,400 preterm births, the researchers noted that the peak onset of labor was 7:45 p.m. in those births were tissue studies revealed definite inflammation of membranes

If there was no evidence of tissue inflammation, labor started at the usual hour even if the infant was born as prematurely as 20 weeks' gestational age or was only in the 10th percentile for weight at full term.

In the report of their findings in Obstetrics and Gynecology (12:87), the team hypothesized that an alternative mechanism accounted for inducing labor when membrane inflammation was present, although the mechanisms for both labor patterns are still unknown. They suggested that although the circadian rhythms of maternal and fetal hormones may trigger normal labor, inflammatory activity may follow a different circadian rhythm. The chemicals released by inflammatory cells, such as prostaglandins, may trigger the altered labor pattern.