Reproductive Factors
Publications under ‘Reproductive Factors’ examine the association of characteristics, interventions and awareness of sexual and reproductive health with fertility and reproductive outcomes.
Among Danish pregnancy planners, shorter menstrual cycle length was associated with longer time to pregnancy. Other menstrual factors, including age at menarche (first menstrual period), how long it took for menstrual cycles to become regular after the first menstrual period, and duration or intensity of menstrual flow, were not associated with fecundability.
We studied factors correlated with menstrual cycle characteristics among Danish women aged 18-40 who had never given birth. Women with low physical activity and heavy alcohol consumption were more likely to have irregular periods. High BMI, smoking, and caffeine and alcohol consumption were related to short menstrual cycles and heavy menstrual bleeding. Women in their mid-to-late thirties had shorter and lighter menstrual flow, but a lower prevalence of irregular cycles, compared with women age 18-25 years.
Among Danish pregnancy planners, women who used oral contraceptives (birth control pill) as their most recent form of birth control had a short-term delay (~3 menstrual cycles) in return of fertility. Long-term oral contraceptive use was associated with slightly increased fecundability.
In the study of Danish pregnancy planners, we observed that fecundability of women is relatively stable with age until decreasing during age 35-40. Men also experience a small reduction in fecundability after age 35. Couples who had intercourse at least twice per week, used non-hormonal birth control (vs. hormonal birth control) before trying to conceive, and had intercourse during the fertile window had higher fecundability. However, these behaviors did not fully offset the decline of fecundability with age.
Among Danish pregnancy planners, oral contraceptive (birth control pill) use before becoming pregnant was not associated with risk of pregnancy loss before 22 weeks.
Among Danish pregnancy planners, pre-pregnancy oral contraceptive (birth control pill) use within 6 months of conception was associated with a small increase in birth weight. However, long-term oral contraceptive use was associated with a small decrease in birth weight.
Among Danish pregnancy planners, women who took longer than 12 cycles to conceive had higher risk of several adverse birth outcomes, including preterm birth, low birthweight, placental disorders, and postpartum hemorrhage, after accounting for fertility treatment. Delayed conception was not associated with risk of small for gestational age birth (low birthweight compared to other infants born at the same gestational age).
Among women who had previously given birth to 1 child, those who gave birth via Cesarean delivery with breech presentation or planned cesarean delivery with cephalic presentation had reduced fecundability compared with those who gave birth vaginally. Emergency cesarean delivery with cephalic presentation was not associated with fecundability.
Among North American pregnancy planners, women with shorter menstrual cycle lengths (≤26 days) had lower fecundability than women with menstrual cycles of 27-29 days. Women who had their first menstrual period at age <12 years had lower fecundability than women who had their first menstrual period at age 12-13 years. Duration and intensity of menstrual flow were not associated with fecundability.
Among women, fecundability decreases with age in an approximately linear manner, with a slightly stronger decline after age ~37 years. After accounting for the age of the female partner, male age was not strongly related to fecundability; however, our study did not include many men over age 45.
Among North American pregnancy planners, lubricant use during intercourse was not associated with fecundability. This association was constant across types of lubricant, including water-based, oil-based, silicone-based and “fertility friendly” lubricants.
Among North American pregnancy planners, many used fertility indicators such as counting days or charting menstrual cycles, measuring basal body temperature, monitoring cervical fluid, using urine luteinizing hormone tests, or feeling for changes in position of the cervix. Use of any fertility indicators was associated with greater fecundability. We did not find consistent evidence of improved fecundability resulting from use of one specific fertility indicator over another.
We compared the fecundability of Danish women who previously only had live births and those who previously only had miscarriages. Women who only had miscarriages took longer to conceive, but had a similar probability of conceiving within 12 cycles of pregnancy attempts.
Use of a menstrual cycle tracking app, especially in combination with observation of one or more fertility indicators (basal body temperature, cervical fluid, cervix position and/or urine luteinizing hormone), may increase fecundability by about 12-20% for couples trying to conceive. We did not find consistent evidence of improved fecundability resulting from use of one specific app over another.
Hirsutism is the presence of excess hair in a male-like pattern, and may indicate an excess of androgen (a hormone). Among North American pregnancy planners, menstrual cycle characteristics including menstrual irregularity, longer cycle length, and heavier menstrual flow were associated with self-reported hirsutism.
Post-partum interval refers to the time between giving birth and attempting to conceive again. Among North American pregnancy planners, long post-partum intervals (≥48 months) were associated with slightly reduced fecundability, independent of female age. Short post-partum intervals (<12 months) were weakly associated with reduced fecundability in some groups, including women with a history of Caesarean delivery and planned pregnancies.
We assessed how North American pregnancy planners changed their behaviors as pregnancy attempt time increases. Some common changes were reducing intake of caffeine, alcohol, and marijuana, and increasing activities to improve chances of conception (e.g., ovulation testing).
Among Danish and North American pregnancy planners, use of some hormonal contraceptive methods was associated with delays in return of fertility. Injectable contraceptives showed the longest delay (five to eight menstrual cycles). However, there was little lasting effect of long-term use of hormonal contraceptive methods on fecundability.
We found important differences in reports of frequency of sexual intercourse between male and female members of couples enrolled in PRESTO. Relationship factors, including being unmarried and longer relationship length, were associated with more disagreement between reports. We also found that when couples’ estimates did not agree, female partners were twice as likely to report more frequent intercourse than their partners.