The tennis pro was competing in the Australian Open when a pregnancy test came up positive – a week before she went on to win the tournament.
In a new interview with InStyle, she insists she was as surprised as her fans, having not seen her now-husband Alexis Ohanian in a month – and she only took the pregnancy test to ‘shut up [her] friend’ who was suspicious.
‘I literally had a cycle just before. So I was surprised when I saw the result and even more surprised when the doctor said I was seven weeks along,’ she told the magazine.
Gynecologists have rushed to clarify that it is not possible to have a menstrual cycle while pregnant, because a period is the shedding of uterus lining that is not needed for pregnancy
However, it is very common for women to experience vaginal bleeding that seems like a period, but is actually the result of something else.
In fact, female athletes are particularly at-risk for bleeding during pregnancy because regular heavy exercise has been shown to affect the regularity of ovulation.
Dr Alyssa Dweck, a New York OBGYN, and Dr Lauren Streicher, a professor of obstetrics and gynecology at Northwestern University, explained to DailyMail.com the various reasons for vaginal bleeding in pregnant women.
YOU CAN BLEED WHILE PREGNANT – BUT YOU CANNOT HAVE A PERIOD
If a woman misses her period it is a sign of pregnancy.
The reason being that menstruation only happens in women of a reproductive age who are not pregnant.
During each menstrual cycle, the uterus builds up a lining of blood, ready for an embryo to implant itself and start growing.
If an embryo does implant, the blood lining stays intact. That is because, once the egg implants, hormones send signals to the tissue in the uterus, telling it that cushion of blood is necessary for the pregnancy.
If no eggs are fertilized, the tissue and blood shed.
FIRST POSSIBLE CAUSE: IRREGULAR OVULATION
‘This happens all the time,’ Dr Dweck told DailyMail.com, when she heard of Williams’ confusion about bleeding while pregnant.
‘It’s possible that she had some sort of ovulation irregularity where she doesn’t ovulate all the time or ovulates irregularly.
In those cases, you can just bleed at any time during your cycle and it seems like a period but it’s just bleeding.
‘That’s why, when people ask if they can have sex without getting pregnant on their period, I say to be careful. You cannot get pregnant on your period, but unless you have a perfectly normal cycle, you can’t be sure. It may not be an actual period.’
Why does it happen?
Few women have a perfectly regular period that comes at the exact same time of the month every month, bleeding the exact same amount, and lasting the exact same number of days.
Most women experience some sort of irregularity due to their fluctuating levels of estrogen, progesterone and testosterone.
It is crucial to have those hormones working in synchronization to keep the cycle ticking. Ovulation is incredibly complex, and requires sufficient amounts of each hormone for each step of the process.
When those hormones are not working in synchronization, it can mean a woman does not ovulate for months, or ovulates at random.
As a result, it can cause ovarian follicles to burst, causing light bleeding, or an increase in estrogen levels, which can also cause light bleeding.
Often, this irregularity is mild, but in some women the fluctuation of hormones is particularly volatile.
Who is most at-risk?
Female athletes often experience this kind irregularity, which studies have attributed to vigorous exercise derailing the balance of hormones.
Other causes of irregular ovulation include PCOS (polycystic ovary syndrome), a disease which slows the development of ovarian follicles, and increasing age.
SECOND POSSIBLE CAUSE: IMPLANTATION BLEEDING
‘It wasn’t a period, it was bleeding. Possibly some implantation bleeding,’ Dr Streicher said.
About a third of women experience this about six to 12 days after conception.
After the sperm fertilizes the egg and becomes an embryo, the embryo moves down to the uterus to implant itself into the uterus wall.
In some cases, this implantation can be imperfect, and causes a little bit of blood to shed down through the vagina.
Usually, this implantation error only triggers light bleeding – much lighter than a regular menstrual cycle – and anything heavy requires medical atention.
DOES IT HAVE ANYTHING TO DO WITH SERENA’S BLOOD PROBLEMS IN PREGNANCY
Possibly, Dr Dweck says.
Women who require anticoagulants, as Williams did, have a higher risk of bleeding during pregnancy.