Photo by Scott Barbour / Stringer / Getty

Serena Williams may have been pregnant when she won the Australian Open, so the New Scientist asked whether her pregnancy may have helped—as if her previous 38 major titles were flukes. But this is a myth that’s been floating around for a while, so let’s talk about what pregnancy really does to an athlete’s body.

A woman’s body produces more blood during pregnancy. A similar change happens to athletes as they train. With more blood, you can supply more oxygen to your muscles. Does that mean pregnancy provides a performance boost?


Too bad there’s no evidence to support that idea. Pregnant athletes’ experiences tend to go the opposite way. I got pregnant while I was training for a marathon, and I found that even though I kept up my training, my fitness went down the toilet. Usually you get faster as you train; I was getting slower. My long run pace slowed down from 10:30 per mile to 12 minutes, and I was consistently the last one to finish group training runs. At five months pregnant, I considered myself lucky to complete the marathon within the six hours the race course was open. Average pace: 13:09.


Why do we slow down even when we have greater blood volume? Probably because a pregnant person’s extra blood and oxygen doesn’t power muscles; it goes to the baby. It seems the people getting excited about the increased blood volume and oxygen uptake have forgotten that important fact. And that makes Serena Williams’s recent title all the more impressive: if she was eight weeks pregnant, she may have been dealing with reduced endurance. And she won anyway.