Telomeres, which are stretches of DNA at the end of chromosomes, protect our DNA and make it possible for our cells to divide. Longer telomeres are associated with longer lives and better health. As people age and as cells divide and replicate, those telomeres shorten.

Given that there is hyper cell production during pregnancy, it makes sense that those telomeres would shorten and, therefore, appear to age dramatically. "During pregnancy, more cells need to be produced for carrying and nurturing the foetus, such as in red blood cells, placental cells, and more," said Dr. Kim Langdon, an Ohio-based retired OB-GYN who writes at Parenting Pod. "In addition, the cells in all organs such as the heart and uterus enlarge. This is known as hypertrophy—and when cells hypotrophy, their telomeres shorten." Meanwhile, the epigenetic age begins to climb. This is an estimate of a person's biological age based on changes in the DNA that are caused by environmental factors, such as toxins and stress. In other words, pregnancy puts a lot of pressure on the body. "I'm not really surprised," Langdon told Healthline about the findings. "Every OB-GYN knows the extreme stress to the system that pregnancy causes." Throughout pregnancy, the blood volume increases by 50 percent as does the cardiac output, which puts strain on the heart. The kidney function increases and the lungs have reduced capacity, which causes breathlessness. Why, then, did the pregnant women seem so much better off? It may all come down to the immunological, hormonal, and physiological changes that take place during pregnancy to support development of the baby. For example, pregnant women experience elevated oestrogen levels, which can lower oxidative stress and prevent damage to telomere length and epigenetic age. Once the baby is born, though, those shifts are no longer necessary.

The study supports previous evidence that women who have had more pregnancies are more susceptible to certain illnesses and have slightly shorter life spans. Earlier this year, researchers from George Mason University found that childbirth could age a woman by as many as 11 years. Grim enough, isn't it?