Sleep, shift work not associated with fecundability, live birth after pregnancy loss

For women trying to conceive after one or two pregnancy losses, sleep duration and timing and shift work were not associated with fecundability or odds of live birth, data published in Fertility and Sterility show.

Because of its potential role in regulating reproductive hormones, sleep is increasingly being considered a key factor in fecundability and fertility, according to study background.

“Furthermore, intermediates of the sleep-wake cycle (melatonin and clock genes) are found in the ovaries and uterus, and thus may be involved in ovulation, embryo implantation at pregnancy establishment and in early gestation through mechanisms in placental development and decidualization,” Joshua R. Freeman, PhD, MPH, a postdoctoral fellow in the Metabolic Epidemiology Branch at the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and colleagues wrote.

“Considering the limited evidence on sleep characteristics, fecundability and live birth, our objective was to evaluate the role of sleep duration, sleep timing and shift work in association with fecundability and live birth in a population of 1,228 women attempting to conceive with a history of one to two pregnancy losses,” they wrote.

Methods

Freeman and colleagues conducted a secondary analysis of the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial. The EAGeR trial enrolled women living in Utah, New York, Pennsylvania or Colorado who were aged 18 to 40 years, had experienced one or two pregnancy losses and were actively trying to become pregnant. Participants were followed for up to six menstrual cycles while attempting to conceive; those who conceived were followed through pregnancy.

Participant-reported typical bedtime, wake time and sleep-onset latency at baseline were used to calculate sleep duration, sleep midpoint — defined as “the midpoint of an average weekend sleep interval and subtracting half the difference between weekend and total sleep durations to correct for sleep debt accrued over weekdays” — and social jetlag, which was defined as the difference in sleep timing between weekdays and weekend days. Weekend days were assumed to be “free” days, but work or school schedules were unavailable to confirm this.

Fecundability, live birth

Final analyses of fecundability and live birth included 1,220 women who completed baseline sleep questionnaires. Of these, 476 (39%) reported sleeping between 7 and 8 hours. Most women worked nonrotating shifts (n = 973) and non-night shifts (n = 903) and had a sleep midpoint before 5 a.m. More than one-third (36.3%) of women had a social jetlag of more than 1 hour.

There were no significant differences in fecundability between women with a sleep duration of 9 or more vs. 7 to 8 hours and sleep midpoints in tertile 3 (midpoint, 4:40 a.m.) vs. 2 (midpoint, 3:36 a.m.). Social jetlag and night shift work were also not associated with fecundability.

Sensitivity analyses excluding shift workers revealed a stronger association between sleep duration and fecundability. Women who slept 9 or more hours had a lower fecundability compared with those who slept 7 to 8 hours (OR = 0.62; 95% CI, 0.42-0.93).

“Separately, per hour increases in social jet lag became stronger in magnitude with low fecundability among women with three or more cycles of pregnancy attempts before study entry,” Freeman and colleagues wrote.

There were 596 live births among the cohort. Analyses showed that preconception sleep duration, sleep timing and shift work were not associated with odds of live birth.

Moving forward, Freeman and colleagues emphasized the need for studies specifically designed to evaluate the effect of sleep on fecundability and live birth in a large cohort.