Dr. Universe,
Do babies open their eyes when they are in their mom’s tummy?
— Neela, 6, Washington state
My litter mates and I were born with our eyes closed. It takes a week or more for newborn kittens to open their eyes and see the world. But newborn humans can open their eyes and look around right away.
I talked about your question with my friend Cindy Brigham-Althoff. She’s a nurse midwife and professor at Washington State University.
She told me that whether unborn babies can open their eyes depends on their fetal age, or how close they are to being born.
Most babies are ready to be born after about 38 weeks of growing and developing. (Or 40 weeks if you count the way doctors do and add two weeks because it’s hard to figure out the exact moment the development process starts.) But some babies are born earlier or later.
For the first eight weeks, an unborn baby is called an embryo. That’s the time when all the major body parts develop, including the eyes. An embryo’s developing eyes are open because the eyelids haven’t formed yet.
From the end of the 8th week on, the embryo is called a fetus. The end of the 8th week is also when the eyelids form and seal themselves shut. That protects the delicate eyes as they grow and develop. They’ll stay that way until the eyelids unseal at 26 weeks (about 6 months).
“They start to be able to open their eyes at 26 weeks,” Brigham-Althoff said. “But they don’t really fully open until 28 weeks.”
So, once the eyelids unseal, what can unborn babies see? Probably not a lot.
For one thing, their eyes aren’t fully developed — and won’t be for a long time. Their eyes will grow and mature for an entire year after they’re born.
The other issue is that a fetus develops inside a pouch-like organ called a uterus. It’s pretty dark in there. Plus, it’s filled with amniotic fluid. Amniotic fluid starts out as mostly water. But then the fetus begins swallowing fluid and peeing it back out.
Even fully developed human eyes don’t see as well underwater — or under-urine. So, a fetus can’t make out details inside the uterus. It’s probably super blurry.
But a fetus can see light.
Their eyes begin to detect light by the 31st week. The dark pupils in the center of the eyes expand or shrink depending on how much light there is. Like yours do.
Brigham-Althoff told me that scientists can use flashlights and special equipment to see how fetuses react to light. That’s how scientists know that babies who are almost ready to be born will turn their heads and move their eyes to look at the light — especially if the flashlight looks like a human face.
That’s probably kind of weird for the fetus. But it’s one way science opens our eyes to the mystery of human development.
Have a science question? Ask Dr. Wendy Sue Universe, WSU’s resident science cat and writer, by email at Dr.Universe@wsu.edu, on her website at askDrUniverse.wsu.edu, via Twitter at @AskDrUniverse or at facebook.com/AskDrUniverse.
