Study question: Is preconception dietary intake associated with reduced fecundity as measured by a longer time to pregnancy (TTP)?
Summary answer: Lower intake of fruit and higher intake of fast food in the preconception period were both associated with a longer TTP.
What is known already: Several lifestyle factors, such as smoking and obesity, have consistently been associated with a longer TTP or infertility, but the role of preconception diet in women remains poorly studied. Healthier foods or dietary patterns have been associated with improved fertility, however, these studies focused on women already diagnosed with or receiving treatments for infertility, rather than in the general population.
Study design, size, duration: This was a multi-center pregnancy-based cohort study of 5628 nulliparous women with low-risk singleton pregnancies who participated in the Screening for Pregnancy Endpoints (SCOPE) study.
Participants/materials, setting, methods: A total of 5598 women were included. Data on retrospectively reported TTP and preconception dietary intake were collected during the first antenatal study visit (14-16 weeks' gestation). Dietary information for the 1 month prior to conception was obtained from food frequency questions for fruit, green leafy vegetables, fish and fast foods, by a research midwife. Use of any fertility treatments associated with the current pregnancy was documented (yes, n = 340, no, n = 5258). Accelerated failure time models with log normal distribution were conducted to estimate time ratios (TR) and 95% CIs. The impact of differences in dietary intake on infertility (TTP >12 months) was compared using a generalized linear model (Poisson distribution) with robust variance estimates, with resulting relative risks (RR) and 95% CIs. All analyses were controlled for a range of maternal and paternal confounders. Sensitivity analyses were conducted to explore potential biases common to TTP studies.
Main results and the role of chance: Lower intakes of fruit and higher intakes of fast food were both associated with modest increases in TTP and infertility. Absolute differences between the lowest and highest categories of intake for fruit and fast food were in the order of 0.6-0.9 months for TTP and 4-8% for infertility. Compared with women who consumed fruit ≥3 times/day, the adjusted effects of consuming fruit ≥1-<3 times/day (TR = 1.06, 95% CI: 0.97-1.15), 1-6 times/week (TR = 1.11, 95% CI: 1.01-1.22) or <1-3 times/month (TR = 1.19, 95% CI: 1.03-1.36), corresponded to 6, 11 and 19% increases in the median TTP (Ptrend = 0.007). Similarly, compared with women who consumed fast food ≥4 times/week, the adjusted effects of consuming fast food ≥2-<4 times/week (TR = 0.89, 95% CI: 0.81-0.98), >0-<2 times/week (TR 0.79, 95% CI 0.69-0.89) or no fast food (TR = 0.76, 95% CI: 0.61-0.95), corresponded to an 11, 21 and 24% reduction in the median TTP (Ptrend <0.001). For infertility, compared with women who consumed fruit ≥3 times/day, the adjusted effects of consuming fruit ≥1-<3 times/day, 1-6 times/week or <1-3 times/month corresponded to a 7, 18 and 29% increase in risk of infertility (Ptrend = 0.043). Similarly, compared with women who consumed fast food ≥4 times/week, the adjusted effects of consuming fast food ≥2-<4 times/week, >0-<2 times/week, or no fast food, corresponded to an 18, 34 and 41% reduced risk of infertility (Ptrend <0.001). Pre-pregnancy intake of green leafy vegetables or fish were not associated with TTP or infertility. Estimates remained stable across a range of sensitivity analyses.
Limitations, reasons for caution: Collection of dietary data relied on retrospective recall and evaluated a limited range of foods. Paternal dietary data was not collected and the potential for residual confounding cannot be eliminated. Compared to prospective TTP studies, retrospective TTP studies are prone to a number of potential sources of bias.
Wider implications of the findings: These findings underscore the importance of considering preconception diet for fecundity outcomes and preconception guidance. Further research is needed assessing a broader range of foods and food groups in the preconception period.
Study funding/competing interest(s): The SCOPE database is provided and maintained by MedSciNet AB (http://medscinet.com). The Australian SCOPE study was funded by the Premier's Science and Research Fund, South Australian Government (http://www.dfeest.sa.gov.au/science-research/premiers-research-and-industry-fund). The New Zealand SCOPE study was funded by the New Enterprise Research Fund, Foundation for Research Science and Technology; Health Research Council (04/198); Evelyn Bond Fund, Auckland District Health Board Charitable Trust. The Irish SCOPE study was funded by the Health Research Board of Ireland (CSA/2007/2; http://www.hrb.ie). The UK SCOPE study was funded by National Health Service NEAT Grant (Neat Grant FSD025), Biotechnology and Biological Sciences Research council (www.bbsrc.ac.uk/funding; GT084) and University of Manchester Proof of Concept Funding (University of Manchester); Guy's and St. Thomas' Charity (King's College London) and Tommy's charity (http://www.tommys.org/; King's College London and University of Manchester); and Cerebra UK (www.cerebra.org.uk; University of Leeds). L.E.G. is supported by an Australian National Health and Medical Research Council (NHMRC) Early Career Fellowship (ID 1070421). L.J.M. is supported by a SACVRDP Fellowship; a program collaboratively funded by the National Heart Foundation, the South Australian Department of Health and the South Australian Health and Medical Research Institute. L.C.K. is supported by a Science Foundation Ireland Program Grant for INFANT (12/RC/2272). C.T.R. was supported by a National Health and Medical Research Council (NHMRC) Senior Research Fellowship (GNT1020749). There are no conflicts of interest to declare.
Trial registration number: Not applicable.