Serena Williams calls post-pregnancy the 'fourth trimester': Why she's right and what women should know

Serena Williams is once again proving herself relatable to new moms -- despite the fact that she’s currently killing it at the French Open in a bodysuit -- by opening up about something very personal: Postpartum depression.

“I remember one day, I couldn’t find Olympia’s bottle and I got so upset I started crying ... because I wanted to be perfect for her,” Williams, 36, told Harper’s Bazaar U.K., speaking of her 9-month-old daughter, Alexis Olympia Ohanian Jr.

“Honestly, sometimes I still think I have to deal with it,” she said. “I think people need to talk about it more because it’s almost like the fourth trimester. It’s part of the pregnancy.”

Williams is not wrong, experts say.

As many as 25 percent of women experience depression after giving birth, according to the American College of Obstetricians and Gynecologists (ACOG).

The ACOG in April released new guidelines on postpartum care to reinforce the period of time after birth that it, like Williams, calls the “fourth trimester.”

The ACOG now recommends that all postpartum women have contact with their OB-GYN or obstetrics provider within the first three weeks after delivery, and that care should continue on an ongoing basis, ending with a “comprehensive postpartum visit no later than 12 weeks after birth.”

What happens in the 'fourth trimester'?

In addition to caring for a new human life, postpartum women are also recovering physically from giving birth, whether by vaginal delivery or cesarean section.

Williams has been very public about the complications she endured after Alexis’ birth, telling Vogue magazine she underwent multiple operations after sustaining a pulmonary embolism the day after she gave birth via emergency C-section.

The 23-time Grand Slam winner said she was forced to spend the first six weeks of motherhood unable to get out of bed.

She bowed out of the Australian Open -- the Grand Slam she won while pregnant with Olympia in 2017 -- in January because she said she was "not where I personally want to be."

While Williams encountered those obstacles with medical care, as many as 40 percent of women who have given birth do not attend a postpartum medical visit, according to the ACOG.

"[There] should be a fourth trimester and providers, midwives, doctors should be seeing women sooner, earlier and more frequently," said Dr. Jennifer Ashton, ABC News chief medical correspondent and an OB-GYN.

In addition to the physical recovery, women in the fourth trimester are also dealing with changing hormones. That time is also when a woman is learning to care for and feed her newborn.

The ACOG recommends new moms have "sustained, holistic support" after birth.

“Our goal is for every new family to have a comprehensive care plan and a care team that supports the mother’s strengths and addresses her multiple, intersecting needs following birth," Dr. Alison Stuebe, lead author of the committee opinion, said in a statement.

Signs of postpartum depression

"There is no shame in this game, not if you’re an Olympian or professional athlete, not if you are the average woman," Ashton said of postpartum depression. "This is very common."

Postpartum depression is not limited to first-time moms and is not limited to even the fourth trimester time period.

As many as 23 percent of pregnant women experience depression during pregnancy, according to the ACOG.

It may be normal as a new mom to feel sad, anxious, or irritable, especially in the first one to three days after giving birth. This is referred to as postpartum blues and usually gets better within a few days or one to two weeks without treatment.

If symptoms worsen and prolong, this may be more suggestive of postpartum depression

Having a history of depression or mental illness puts women also at risk of having postpartum depression.

Women and their family members should be alert to signs of postpartum depression, including tearfulness and crying, anger and irritability, anxiety, guilt, feeling detached from the baby and fantasies of escaping new life as a mother.

If postpartum depression continues to persist and leads to significant effects on one's quality of life, it is important to see a healthcare provider.

What new moms can do

The good news is that postpartum depression can be treated and women can fully recover, according to Ashton.

The key for women and their doctors is to "address it head-on," she said.

Treatment for postpartum depression includes everything from medication to psychotherapy and support groups.

Postpartum depression and diet

Some research has also shown that diet can be part of the toolkit used to treat postpartum depression.

Eating foods like herbs and legumes -- staples of the Indian confinement diet -- after giving birth may lessen women’s symptoms of postpartum depression and anxiety, a small study conducted in Singapore found.

Though the study is too small to apply to all women, most experts agree what postpartum women eat does affect their mental well-being.

"Anybody who has really tapped into their mood and mental state and then looked at what they've eaten can corroborate [that diet affects mood]," said Dr. Jennifer Lang, a Beverly Hills, California-based OB-GYN, whose book, "The Whole Nine Months," focuses not just on pregnancy but also the fourth trimester.

Postpartum women are advised to follow the U.S. government's 2015 to 2020 Dietary Guidelines for Americans, which focuses on fresh fruits and vegetables, whole grains, and getting nutrients from food instead of supplements.

Lang also recommends that new moms eat a high-fiber and low-sugar diet to help with healing, and also drink lots of water, especially if they are breastfeeding.

Limiting caffeine and avoiding foods high in sugar can also help new moms sleep more soundly, according to Lang.

"The better you are eating and the better you are sleeping, the better you're going to feel about your body in general and new motherhood in general," she said.

What partners and family members can do

Postpartum depression is something that affects not just mothers but their families as well.

Partners then are critical in both identifying and helping to treat postpartum depression, according to Ashton.

"They need to support that person emotionally and physically," she said. "This is a major issue and it doesn’t just affect that woman, it affects her entire family."

Ways that partners can help include accompanying the new mom to medical appointments, helping with child care, becoming educated on postpartum depression and, most importantly, not leaving the new mom alone if you're concerned she is struggling.

Williams' husband, Reddit co-founder Alexis Ohanian, announced in February that he would step down from his daily role at Reddit, after utilizing the company's 16-week paid paternity leave.

“I was a believer before, but now I wholeheartedly believe that every single dad should take it," he told Fortune, adding that the time off was helpful in light of Williams' delivery complications. “That really put into perspective how important these policies are.”