Babies cry in the womb — and 18 other surprising facts I learned when I became a dad

newborn baby parents ann price photography

Happy father's day to all the dads and dads-to-be out there. When I learned I was going to be a new dad, I was floored ... and scared.

To counter the fear of becoming new parents, my wife and I read. And read and read and read.

We rounded up about a dozen science-backed books, scanned countless research studies, downloaded pregnancy apps, and shared hundreds of articles with each other over the following months.

During that flood of information, a handful of surprising facts floated above the rest, and I've collected them here.

What follows may not surprise an obstetrician, or even seasoned parents, but it nonetheless highlights the extraordinary human journey that is pregnancy.

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Fertilization is 1-in-100-million affair.

Men release about 100 million sperm each time they ejaculate, though the semen of some especially fertile men can contain hundreds of millions of sperm.

But only a few hundred may ever reach a woman's egg. Special receptors on the surface of an egg make sure only one gets in. (Fraternal twins occur when two sperm fertilize two eggs, while identical twins occur when one sperm fertilizes one egg and it splits into two embryos.)

Source: US National Library of Medicine/MedlinePlusOakland University

Babies are about 15 days younger than the length of a pregnancy.

Since 1836, doctors have marked the first day of a woman's last menstrual period as the first day of pregnancy, or "gestational age," not when a sperm fertilizes an egg.

Ovulation happens about two weeks after a period, on average, and fertilization happens within 24 hours of that. This means if you're eight weeks pregnant, your baby is about six weeks old.

Doctors still use gestational age, not ovulation age (also called postconceptional age) because it's hard to detect ovulation and fertilization even more so. Periods, meanwhile, are hard to miss — and easier to notice when they've gone missing.

Sources: American Pregnancy Association, "Williams Obstetrics", Business Insider

Most women aren't pregnant for 9 months.

Nine months works as a very rough estimate, but this oft-said number can lead to a number of misconceptions.

First, it's not a target; a healthy pregnancy can vary as much as five weeks around a 40-week due date. In fact, only 4% of women deliver on their 40-week due date.

The typical pregnancy — measured from ovulation, not the last menstrual period (which is standard) — actually lasts about eight months and 24 days, not nine months.

Source: Business Insider

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