Why amniotic fluid levels during pregnancy matter
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At her 30-week prenatal checkup, Ali Feeney’s belly was measuring small, so her obstetrician sent her for an ultrasound. She went to the hospital for the scan on her lunch break the day she was training her maternity leave replacement, but didn’t return to the office. When the ultrasound showed Feeney’s amniotic fluid was dangerously low, she was quickly given a non-stress test to check on the baby’s movement and heart rate. If the results were abnormal, she was warned she may need an emergency C-section.
“It was stressful and I had a million questions,” says the Ottawa mom, who was living in Vancouver at the time. “I was wondering, Is it something I did? Is it because I have a cup of coffee a day?”
Upon checking, the baby’s heart rate was fine and she was moving normally. But Feeney was immediately put on modified bed rest and urged to drink lots of water to help build up her fluid. From that moment on, Feeney says she set a goal for herself of drinking 20 glasses of water a day, and she gave up her morning coffee. (Drinking a normal amount of water per day—eight glasses—is fine during pregnancy. It was Feeney’s personal choice to cut coffee altogether. Limiting caffeine to 200 to 300 mg a day is the recommendation during pregnancy.)
Instead of spending her third trimester wrapping up things at the office, browsing for baby gear in boutiques and going for long walks on the beach with her husband, Feeney worked remotely, shopped online and went to the hospital two or three times a week for monitoring.
“Amniotic fluid provides protection, cushioning and a nice, warm environment for the baby to thrive and grow,” says Kenneth Lim, head of maternal fetal medicine at BC Women’s Hospital in Vancouver. “It’s also a rough indicator of the baby’s health status.”
Amniotic fluid levels are assessed during routine ultrasounds. If your last ultrasound was at the 20-week mark, and you don’t have another one scheduled, you would only find out about a fluid level issue later in pregnancy if you or your provider notices other concerns and an additional ultrasound is performed. (For example, if your bump isn’t measuring consistently with gestational age; if there’s been a decrease in fetal movement; if you have high blood pressure; or if your doctor or midwife suspects the baby might be breech.)
There are different techniques for measuring amniotic fluid, but the Society of Obstetricians and Gynaecologists of Canada (SOGC) recommends measuring—on an ultrasound image—the single deepest pocket of fluid. A pocket deeper than eight centimetres and wider than one centimetre means you have too much fluid, known as polyhydramnios. A pocket less than two centimetres deep and one centimetre wide is considered too little, or oligohydramnios. Less than 10 percent of women will have oligohydramnios or polyhydramnios diagnosed on an ultrasound. Both conditions can cause complications or be a sign of an underlying condition in the baby or mother.
Amniotic fluid comes from different sources: the fetus, the placenta, and the mother. In the second trimester, urine becomes the main ingredient when the baby begins to swallow the fluid and her kidneys start working. Amniotic fluid helps the baby’s bones, muscles, lungs and digestive system develop, and ensures the umbilical cord doesn’t get compressed. At 20 weeks pregnant, women have about 400 millilitres of fluid. The volume doubles to 800 millilitres at 28 weeks gestation, and remains at that level until 37 weeks, when it starts to go down. When babies are born, they have 400 to 500 millilitres in their amniotic sac—that’s about two cups of fluid.
“The fluid around your baby in the uterus is a balance between production and removal,” Lim says. “Any time we diagnose high fluid or low fluid, it adds another question, which is, Why?”
The most common explanation for low fluid is a leak in the amniotic sac. The mother may also be dehydrated or there may be a problem with the placenta. Sometimes the baby has kidney problems or a urinary track blockage, or excess fluid can build up when the baby has trouble swallowing due to a birth defect. Diabetes in the baby or mother can also lead to polyhydramnios.
Often, there is no known cause, as was the case with Feeney. By 36 weeks, she had increased her fluid to a normal level, but her baby was breech, likely because she didn’t have enough water to help her get into position. Feeney had a scheduled C-section at 38 weeks and baby Sloane was born healthy and without complications.
“There are going to be many cases where there’s high fluid or low fluid and the kid is perfectly fine," says Lim. "We always have to remember that it doesn’t necessarily mean that there’s something wrong. But the worse it gets, the more likely there is truly something wrong that needs to be managed by a health care professional.”
Usually, women with high or low fluid will be closely monitored. In serious cases, amniotic fluid may need to be removed with a needle or—rarely, in very special circumstances—fluid (usually a saline solution) can be added through a catheter, says Lim. Sometimes, a woman's body may be tricked by the excess fluid into thinking it’s time to deliver, causing premature labour.
That was Stephanie Somers’s biggest fear. After learning that she had gestational diabetes with her second child, a diagnosis of polyhydramnios soon followed, at 29 weeks. She was warned some of her fluid may have to be removed. By 37 weeks, the Sidney, BC, mom was measuring 42 weeks and her baby was also breech —because she had so much extra water to bob around in. “That’s when it got really scary,” Somers says. “I was told that if my water breaks, I had to get to the hospital immediately.”
Doctors were worried about cord prolapse, when the umbilical cord comes out before the baby, due to the baby’s position and the volume of fluid. As soon as Somers felt a tickle of a contraction, she headed into the hospital and had a C-section. “Wow! That’s a lot of water,” someone in the delivery room said as baby Delilah was born.
While women with oligohydramnios and polyhydramnios are at greater risk of preterm labour, C-sections and stillbirth, the majority of mothers have healthy babies. “In most cases, everything is going to turn out fine,” Lim says. “It’s rare to have bad outcomes in relation to abnormalities of amniotic fluid.”