Heavy Use of Tobacco and Caffeine Are Among Factors That May Reduce a Woman's Chance of Conceiving

Susan London

First published online:

For couples trying to conceive, certain negative lifestyle factors are associated with an increased time to pregnancy and an elevated risk of not conceiving in the first year.1 In an observational study of pregnant women and their partners, a couple's risk of not conceiving in the first year of unprotected intercourse was raised when women smoked heavily (relative risk, 3.6), had a heavy intake of coffee or tea (1.7), or were above or below normal weight (2.2-6.9); when male partners had a heavy alcohol intake (2.2); and when the couple had a low standard of living (1.6). The risk increased with each additional factor, and the probability of being pregnant after a year dropped from 93% for couples who had one of the factors to 38% for those with four or more.

Researchers gave questionnaires to consecutive women attending prenatal clinics in two British teaching hospitals to obtain information about their age, time to pregnancy (i.e., from discontinuation of birth control use until conception), gynecologic and pregnancy history, contraceptive use and frequency of intercourse. The questionnaires also asked for information that the researchers used to assess negative lifestyle factors—for women, underweight (body mass index less than 19 kg/m2), overweight or obesity (25-39), or severe obesity (greater than 39), and heavy coffee or tea intake (seven or more cups a day); for both partners, heavy smoking (more than 15 cigarettes a day), heavy alcohol consumption (more than 20 drinks a week), any recreational drug use and low standard of living.

Analyses were based on 1,976 women and their partners. On average, the women were 27 years old and had partners who were 30 years old. The women's mean number of previous pregnancies was 1.5. Couples had intercourse an average of two times per week. Overall, 81% of women became pregnant by the end of the first year; about half of the rest conceived in the second year. Women who did not conceive within one year were significantly older than those who did, had older partners, weighed more and smoked more; their partners smoked and drank more than the partners of women who conceived within one year.

In an analysis adjusted for factors that potentially affect conception, the time to pregnancy differed significantly among women who were nonsmokers, light smokers and heavy smokers (nine, 11 and 19 months, respectively), and among women whose partners were nondrinkers, light drinkers and heavy drinkers (nine, 10 and 17 months). Women with a normal weight became pregnant sooner (within seven months) than women who were underweight (26 months), overweight or obese (11 months), or severely obese (14 months). Couples with a high standard of living conceived sooner than those with a low standard (seven vs. 11 months). Overall, the time to pregnancy increased with total number of negative lifestyle factors, from three months for couples with none to 21 months for couples with five or more.

In a second adjusted analysis, couples' risk of failing to conceive within the first year was elevated when women smoked heavily (relative risk, 3.6) or had a heavy intake of coffee or tea (1.7). Relative to couples in which the man did not drink, those in which the man drank heavily had more than two times the risk of not conceiving within the first year (2.2). Couples in which the woman was underweight had a sharply elevated risk (4.8); risk was also raised when the woman was overweight or obese (2.2) and was markedly increased when she was severely obese (6.9). Couples with a low standard of living had a 60% greater risk of not getting pregnant within a year than couples with a high standard (1.6). Compared with couples who had no negative lifestyle factors, those with two had 3.3 times the risk of not conceiving within the first year, and the differential climbed steadily to 7.2 for those with five or more. The cumulative probability of conceiving within a year decreased steadily from 93% among couples with one negative lifestyle factor to 38% among those with four or more.

The researchers note that because couples who stopped trying to get pregnant were not included in the study, the apparent harmful effects of the lifestyle factors studied may be underestimates. They contend that while couples often disregard the impact of lifestyle factors on fertility, the data suggest that adopting a healthy lifestyle would more than halve the proportion of couples who are unable to conceive within one year. In the long term, such a reduction could lead to a "substantial decline in the referrals for medical investigations and fertility treatments," they conclude.

—S. London


1. Hassan MAM and Killick SR, Negative lifestyle is associated with a significant reduction in fecundity, Fertility and Sterility, 2004, 81(2):384-392.