The science behind why swimming and pregnancy go together

Lindsy Talbert’s belly gets a little bigger every week. As it grows, the budding mother employs new tricks at swim practice to accommodate her developing bump. “I’ve started doing flip turns with my legs a little wider,” says the 27-year-old member of Longhorn Aquatics Masters in Austin, Texas. Nearly seven months into her first pregnancy, Talbert logs three pool workouts a week, easily making intervals in the same lane she’s always led. Carrying another human hardly seems to hinder her swimming. “I still go about the same speed, but I’ve lost some of my endurance,” she says. Talbert, who works butterfly laps like a porpoise and executes sprint sets with fervor, says that when it comes to pushing herself in the pool, her obstetrician is all for it.

Swimming Through Pregnancy Gets the Green Light

Doctors have long promoted exercise during pregnancy. “We know that women who exercise while pregnant have better outcomes,” says Barney Lynch, an obstetrician-gynecologist at the Austin Regional Clinic. “They have a lower incidence of gestational diabetes and decreased rates of preterm delivery and large-for-gestational-age babies,” says Lynch, who also swims Masters with Longhorn Aquatics. Active pregnant women, he adds, tend to have fewer caesarean and operative vaginal deliveries and faster postpartum recovery times.

Swimming, with its non-weight-bearing and temperature-regulating qualities, ranks high among pregnant women as a favorite form of exercise, especially as delivery dates draw near. Lynch has good news for swimmers who wonder how time in the water affects a pregnancy. “Pregnant women who participate in aquatic exercise have decreased levels of lower back pain and lower leg edema, which is always a concern,” he says. Lynch references a study published in the Journal of Obstetric, Gynecologic & Neonatal Nursing in 2006 that showed women who chose water aerobics over land-based exercise took fewer sick days during their pregnancies because they experienced less lower-back discomfort.

For swimmers concerned about how pool chemicals affect pregnancy, Lynch has more promising information. “There really is little to no evidence suggesting that chlorine and other pool chemicals affect fetal growth and development,” he says, referring to a paper published by Spain’s Centre for Research in Environmental Epidemiology on the health impacts of disinfection byproducts in swimming pools. The paper indicates that swimming in treated pools during pregnancy is not associated with an increased risk of preterm delivery, low birth weight, or congenital abnormalities. But how does the strenuous exertion of a Masters workout affect a developing fetes? Most of the research addressing fetal reaction to maternal exercise has focused on fetal heart-rate changes and birth weight. Lynch points to a study published in Obstetrics & Gynecology in March 1991 that compared fetal responses to maximal swimming versus cycling exercise during pregnancy. “All of the women in the study delivered healthy, normal-weight babies at term, but cycling caused transient fetal bradycardia more often than swimming,” he says. (Fetal bradycardia is an abnormally low fetal heartbeat.) The study also noted that the hydrostatic effects of water link swimming exercise to smaller plasma volume decreases among pregnant women than typically seen with land exercises, which might result in better uterine and placental blood flow.

Since physical exertion can cause a decrease in total uterine blood flow, and poor uterine profusion can lead to fetal bradycardia, doctors have generally recommended keeping maternal heart rates below 140 beats per minute during exercise. Although, “it’s fine for pregnant women to do a hard set at swim practice,” Lynch says, “as long as they pay attention to their bodies, stay hydrated, and rest when they need it.” Pregnant swimmers don’t need to continually check their pulses either, he says, and they can swim all four strokes in any type of distance or sprint workout—but they might feel the effects of a hard set sooner than they used to.

What to Watch For

Mary Hughes, who swims with Lynch at Longhorn Aquatics, has broken the doc’s only rule for expectant swimmers: No diving! “I only went off the blocks once during a race many years ago, and it was a mistake,” Hughes says looking back. Her belly dropped to within an inch of the pool bottom as she left the blocks. “I was young, and I thought I’d be fine,” she says. Luckily, she and her son, who’s now 32, finished that race unharmed. Hughes went on to swim through three more pregnancies and credits the camaraderie and peacefulness of swimming for making her a better mother.

Errant arm strokes or kicks to the belly pose another major no-no. “You really want to minimize abdominal trauma,” says Tossy Fogle, a perinatologist with Georgia Perinatal Consultants in Atlanta. “A hit to the stomach could cause an abruption, or separation of the placenta from the uterus, and may necessitate an early delivery.” She also recommends avoiding breath-control sets while pregnant. “You don’t want mom to become anoxic, because it affects the baby’s oxygen,” she says.

Apart from using swimming as a safe way to maintain fitness and manage weight during pregnancy, Fogle’s patients have found another purpose for the sport. “I have many patients with breech babies who will swim laps or do summersaults underwater to try to naturally turn the baby,” she says, noting that there’s no science behind this practice. “It’s just a maneuver my patients attempt if their babies haven’t flipped by 37 weeks,” she says.

Fogle has a few final recommendations: “Hydrate, hydrate, hydrate!” Consuming plenty of fluids can help prevent vasovagal syncopal (fainting) events, dehydration, and preterm contractions. Fogle also notes that patients with certain conditions such as preeclampsia, cervical insufficiency, placenta previa, multiples, or chronic medical problems generally shouldn’t exercise during pregnancy.

Swimming for Emotional Support

Other concerns can attract expectant mothers to the water. Katie Ryan didn’t fret for a second over pool chemicals, kicks to her abdomen, or an elevated heart rate when she went looking for a way to stay fit during her first pregnancy. At 35, the triathlete worried most about how she would get her endorphin fix and stay connected to an athletic community over nine long gestational months.

Ryan started attending Masters practice almost daily at Western Hills Athletic Club in Austin. “I had underestimated the community of swimmers before my pregnancy,” says Ryan, who always thought of herself as more of a runner. Yet at two weeks past her due date, swimming provided the only comfortable way for her to remain active and socially linked. “I swam up to two days before I delivered, and everyone treated me so well that I became devoted to Masters,” she says. “I think I’m going to continue swimming regularly from now on.” Ryan found it comforting to surround herself with other women who also swam through their pregnancies. What better place than a women’s locker room full of healthy female athletes to find perspective on the life changes awaiting a new mother?

Ryan touches on another important aspect of swimming while pregnant. “In the early months, I went through a long stretch of time where I felt unfit and I didn’t recognize my body. I wasn’t really showing yet, but I was bigger all over, and I had to buy a size up in my swimsuit,” she says, noting that a quick look at maternity suits left her content to stick with the former option. For all the good aquatic exercise does, pregnancy still presents a time when a woman’s body goes through drastic changes—rarely more on display than when swimsuit-clad on a pool deck. “I had to remind myself that my expanding waistline went along with growing a human being so that I didn’t suffer from the same high-school-girl body-image stuff I might endure if I weren’t,” Ryan says. In time, Ryan grew comfortable with her temporary bulge and welcomed the opportunity to stretch out her belly on long pull and kick sets. “We spend most of practice submerged anyway,” she says, laughing, “and the water is very forgiving.”

As Ryan’s body morphed, her swim performance did, too. “I stayed with my lane until 36 weeks, when I finally gave in and moved over,” she says. She thought she might sink on backstroke but never did, and she gave herself permission to slow down and enjoy guilt-free rest at the wall when she needed it. New swim goals accompanied each week of pregnancy as well. “I stopped trying to get faster and I started working toward getting strong for giving birth.”

Postpartum Recovery

A few weeks ago, Ryan delivered a healthy baby girl at her home in Austin. “I labored for nearly 11 hours, and endurance-wise, it was more than I ever expected,” she says, adding that she would rather do 10 Ironman triathlons than give birth that way again. But swimming, she maintains, made her stronger and better prepared for natural childbirth.

Doctors’ orders now call for at least a month-long cease in intense physical activity so Ryan can heal. This might present the hardest challenge she’s faced in 40 weeks. “With no exercise, I’m not getting the endorphins like before,” she says, a little worried. Then, she shifts and says, “You know what? It’s a forced taper that I need, and I am getting something special from bonding with my baby.” She’s also benefiting from a boost in oxytocin, the hormone that helps with milk production—one of the same chemicals released in the brain when a person falls in love. Plus, she knows that calories burned during breastfeeding can make up for some missed workouts.

Ryan also takes comfort knowing that rest can send her back to the pool stronger than before. “I have so many friends who had their best races eight or nine months after giving birth,” she says excitedly. That notion, coupled with her love for the magnificent human nestled in her arms, carries Ryan through her new workout regimen of caring for a newborn.


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