Some women experience eye and vision changes during pregnancy.Credit: Mayte Torres / Getty

In 2015, 21% of births worldwide were by caesarean section1, more than double the number two decades ago. When warranted, the procedure saves lives, but it is major surgery and comes with numerous risks, including maternal death, bleeding and uterine rupture and, in subsequent pregnancies, stillbirth or preterm birth. Consequently, efforts have been underway for years to understand what is driving this trend and to identify women who are receiving the intervention unnecessarily.

Part of Nature Outlook: The eye

Women with myopia — difficulty seeing objects in the distance (also known as short-sightedness) as a result of the eye growing too long from front to back, a lens that is too thick or curvature issues with the cornea — undergo a disproportionately high number of caesareans, particularly in Eastern Europe. Researchers at the University Clinical Hospital Rijeka in Croatia, for instance, found that, over a 10-year period at the hospital, women with myopia were 1.5 times more likely to give birth by caesarean than were women who were not myopic2. Women requiring the strongest prescription lenses were nearly four times more likely to have a caesarean.

It was thought that, during the pushing stage of labour, short-sighted women might be at risk of retinal detachment — a condition in which the retina separates from the layer underneath, at the back of the eye, which can cause permanent vision loss or blindness. However, mechanistically or physiologically, there is no link to support this, says Samer Elsherbiny, a consultant ophthalmic surgeon at Warwick Hospital, UK. “This is a prevalent urban myth.”

That myth persists for several reasons. People who are very short-sighted can have thinner retinas, which can tear more easily if there are any changes to the gel-like material inside the eye, called the vitreous humour, leading to detachment. But although venous pressure in the eye increases when a woman pushes during childbirth, explains Elsherbiny, this pressure has no effect on the vitreous humour.

Pregnancy can trigger changes to the eyes and vision owing to fluctuations in hormones, metabolism, fluid retention, blood circulation and the immune system. These changes can cause the thickness and curvature of the cornea to increase, for example, which can alter vision. Optometrists therefore generally advise pregnant women to postpone getting new glasses until several weeks after they have given birth, and to delay decisions on LASIK surgery — a procedure in which doctors use a laser to change the shape of the cornea — for several months. Some doctors also advise women to avoid becoming pregnant in the year after the surgery, or even to put off corrective eye surgery altogether until after they have had children, but that advice might be outdated, says Alejandro Fernández-Montero, an occupational physician at the University of Navarra, Spain, who found in 2017 that women are at lower risk of myopia development or progression while they are pregnant3.

During labour, women are often encouraged to perform the Valsalva manoeuvre — forced exhalation while the airways are closed — to increase the chest and stomach pressure in order to push. This increase in pressure does not cause retinal detachment, but can lead to capillaries in the eye rupturing and affecting vision, a condition known as Valsalva retinopathy. But it is generally not serious and typically clears up on its own.

Even pregnant women with pre-existing eye problems such as diabetic retinopathy, a condition caused by high levels of sugar in the blood that damages the retina, are not routinely recommended a caesarean, says Janet Sunness, a retina specialist and medical director of the Richard E. Hoover Low Vision Rehabilitation Services in Towson, Maryland. This advice also extends to women in the disease’s more-advanced stages, when the abnormal blood vessels can lead to bleeding or retinal detachment. “The evidence is not strong enough for them to have a C-section,” Sunness says.

But the lack of evidence has not prevented numerous women from having caesareans because they have an eye condition. The exact number is hard to pinpoint, but, in 2010, researchers in Poland reported that 2% (100 of 4,895) of caesareans performed between 2000 and 2008 at Dr Jan Biziel University Hospital No. 2 in Bydgoszcz were carried out following a written recommendation from an ophthalmologist4. In nearly half the cases, eye problems were the sole reason for the procedure, with myopia topping the list of ophthalmological reasons.

Efforts are underway to reduce the number of caesareans carried out owing to eye conditions. In 2003, following the results of the Croatian study, which showed that almost 40% of women with high myopia in one hospital were undergoing caesareans, the then-director of the hospital’s department of obstetrics and gynaecology, Oleg Petrović, changed hospital policy to say that high myopia alone was not sufficient as a reason for a caesarean.

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To ensure that this decision did not negatively affect either women’s eye conditions or pregnancy outcomes, Petrović carried out a second study between 2003 and 2007, involving 240 women. His team showed that, whether the women had low, medium or high myopia, the policy change did not increase the number of eye complications5. In 2015, the University Hospital Trnava in Slovakia similarly ceased performing caesareans for opthalmologic reasons. Between 2010 and 2014, before the new policy was instituted, caesareans linked to eye conditions such as myopia accounted for 1.8% of all such surgeries at the hospital6.

In some places, however, the practice remains common, such as in rural areas and small hospitals in Romania, where both doctors and patients are accustomed to the practice, says Corina Taban, an ophthalmologist at Dr Victor Gomoiu Children’s Clinical Hospital in Bucharest. It is the duty of obstetricians who are familiar with this issue to educate their colleagues, says Petrović. Breaking the faulty link between myopia and caesareans, he says, “could result in a reduced number and frequency of C-sections worldwide, as well as an improved maternal mortality and morbidity”.