Women who drank five or more cups of coffee a day were about 50% less likely to get pregnant through in-vitro fertilization (IVF) than non-drinkers, according to a recent Danish study.
“Although we were not surprised that coffee consumption appears to affect pregnancy rates in IVF, we were surprised at the magnitude of the effect,” said lead researcher Dr. Ulrik Schiøler Kesmodel of the Fertility Clinic of Aarhus University Hospital, in Denmark, in a statement.
For the study, presented at the annual meeting of the European Society of Human Reproduction and Embryology in Istanbul, Kesmodel and his colleagues followed nearly 4,000 women receiving IVF or intracytoplasmic sperm injection (ICSI) treatments in a large Danish fertility clinic. The women reported their coffee consumption at the start of treatment and at the start of each cycle. The researchers controlled for a variety of factors: the women’s age, smoking and alcohol consumption, the cause of their infertility, weight, ovarian stimulation and number of retrieved embryos.
Their findings showed that the relative chances of pregnancy were cut in half for women who drank more than five cups of coffee per day — “comparable to the detrimental effect of smoking” the authors noted — but there was no effect in women who drank less coffee.
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“There is limited evidence about coffee in the literature, so we would not wish to worry IVF patients unnecessarily,” said Kesmodel in a statement. ”But it does seem reasonable, based on our results and the evidence we have about coffee consumption during pregnancy, that women should not drink more than five cups of coffee a day when having IVF.”
The assumption is that it’s the caffeine in coffee that may interfere with IVF success, but as Kesmodel told the BBC, there are so many substances in coffee, it’s hard to know for sure. However, researchers have long sought to understand whether caffeine affects fertility, and previous studies have found mixed results. Some data suggest that coffee drinkers are more likely to miscarry, while others have found the opposite. Some studies have also linked high caffeine consumption with lower odds of pregnancy, low birthweight and preterm birth, but a 2009 Cochrane review of gold-standard trials couldn’t confirm any benefits of avoiding caffeine during pregnancy.
Women who enjoy a cup-o-joe in the morning shouldn’t fret. “The fact that we found no harmful effects of coffee at lower levels of intake is well in line with previous studies on time-to-pregnancy and miscarriage, which also suggest that, if coffee does have a clinically relevant effect, it is likely to be upwards from a level of four-to-six cups a day,” said Dr. Kesmodel.