Smoking dramatically lowers the likelihood a woman will manage to conceive naturally. In each of 12 separate studies, investigators concluded women who smoked were far more likely to be unable to conceive, and when the 12 studies were merged together investigators determined women who smoke were 60% less likely to conceive than those who avoid smoking.
While many of us believe IVF solves the issue of infertility, the reality is most IVF cycles don’t work and when women smoke they’re nearly twice as likely to fail according to a dataset from over 20 studies.
That nearly 2x drop in success for female smokers shows up for male smokers too. A German team looked just at this issue in 2003 and showed that amongst over 700 couples, IVF cycles had far lower pregnancy rates when the man smoked (even if the woman didn’t). As you can see from the data below, even when couples resorted to using ICSI to fertilize their eggs during IVF, it didn’t close the gap in success rates between male smokers and non-smokers.
There is no shortage of data on how caffeine impacts a woman’s ability to conceive but there is a shortage of useful data. Nearly all of the studies are retrospective, subject to recall and self-reporting bias, and it can very hard to correct for confounders like smoking or the male partner’s intake.
For women trying to conceive naturally, the data conflicts about how harmful coffee intake is. Below is a snapshot of the better run studies and as you can see, it’s hard to draw conclusions. Today most experts say one to two cups of coffee per day is probably OK, but there is certainly data to suggest that number is too high or too low.
Of the six quality studies on coffee intake and ability to conceive during IVF, five suggest moderate caffeine intake has no bearing on outcomes. For that reason, the American Society of Reproductive Medicine’s current stance is that roughly one to two cups of coffee per day is permissible.
Once pregnant, the data suggests caffeine intake is unhelpful, but the data is not totally universal. In our mind, below are the better studies on the subject. All things equal it’s probably best to avoid caffeine consumption at this period. For context of the data below, 1 cup of coffee equates to about 100 mg of caffeine.
Similarly, above two cups of coffee per day for men and it seems like birth rates may begin to suffer. Below you can find data from a survey of 500 couples trying to conceive and amongst those with a male drinking two or more cups of coffee per day, the risk of miscarriage was higher.
In the context of a couple doing IVF, male consumption of caffeine probably begins to have an impact after around 200 milligrams per day, or about 1.5 – 2.0 cups of coffee per day. Below is the work from the team at Massachusetts General Hospital, who observed only a small number of patients (almost too small for our liking), but did a nice job isolating variables (like smoking and alcohol consumption) and looked at the real world endpoint of live birth rate.