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.
Our goal is not just to conceive, but also to have a healthy baby. Below we’re going to show you data on how alcohol impacts a woman’s ability to conceive. But let’s not confuse this for any possible implications to the offspring. It’s safest to avoid drinking any alcohol when trying to conceive during a woman’s fertile window. And if a woman conceives, doesn’t realize it, and continues to drink, the results can be harmful.
Most data suggests a woman can have a drink or two per day while trying to conceive naturally without harming her odds of success.
Probably the best study we have seen on the subject followed 6,000 Danish women trying to conceive naturally and charted their self-reported alcohol intake. Investigators noticed a trend that women consuming 14 or more alcohol beverages per week were 18% less likely to conceive in a 12 month stretch, but beneath that 14 drink per week threshold made no difference. It did not matter whether these women drank wine, beer, or spirits.
The Nurses Health Study, a well-respected study that followed the habits and outcomes over decades of 125,000 women, also looked at this question. Investigators determined that women who had one drink per day had a slightly increased risk of “anovulatory infertility” (unable to conceive due the inability to ovulate), but after correcting for confounders, that difference disappeared.
As for women trying to conceive through IVF, two credible studies observed that moderate alcohol intake in the year before the first cycle had no correlation with live births rates.
However, alcohol consumption in the immediate run-up to fertility treatment clearly has a negative effect. Below Klonoff-Cohen showed that having one extra glass of wine per day in the lead-up to treatment raised the risk the cycle would fail by 4 - 6x depending upon how close to the cycle the woman’s drinking drinking occured. Unfortunately, the study is older and incorporates fertility treatments that haven’t been used in ages. But most believe the effect is striking enough to overcome the studies shortcomings and to make it noteworthy.
Once a woman believes she may have conceived, she should stop drinking alcohol immediately and follow the guidance of her doctor.
We have little good data on how alcohol consumption impacts a man’s ability to conceive naturally, but it seems clear that increased levels of intake can hamper the concentration of sperm in a man’s semen sample. Below you will see data from over 1,200 Danish men ages 18 - 20 showing that after certain thresholds (like 25 drinks per week) sperm concentrations go down.
Amongst fertility patients, the data is extremely divided. Studies like Klonoff-Cohen’s reveal men who consumed more alcohol had lower IVF success rates. But a well-respect team out of MGH in Boston showed that men who consume 1.4 drinks per day have higher success rates than those who abstain.