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Conception from the Beginning

Reexamining the Birds and the Bees

By Melinda Copp

Everyone knows how to make babies, and it isn't exactly molecular biology. However, after you do the deed, the whole process of actually creating a baby becomes much more complex. And this process is, literally, molecular biology.

Can you imagine how a sperm and egg that are so small they are almost invisible grow into a 7-pound baby? The process is delicate and incredible and part of being human.

Scientists have studied the way babies go from a fertilized egg to human being, and they have documented each step of the nine-month process. But, by far, the most remarkable changes occur before you even know you're pregnant.

After having sexual intercourse, your partner's sperm travels through the opening of your cervix and into your uterus. The sperm are making their way toward your fallopian tubes. Some of them will head to the left and some will head right, and because you only ovulate on one side each month, some of the sperm cells will head in the wrong direction.

It takes nearly half a day for the sperm cells to reach the fallopian tube. If there's an egg in one of the tubes and one of the sperm reaches it, then fertilization will occur. But if the sperm cells don't find an egg, they will die.

This is not an easy journey. Some die along the way, and some choose the wrong fallopian tube. Only a fraction of the millions of sperm cells released during intercourse ever make it to the egg. So the day after intercourse, by dinner or so, fertilization will have occurred. However, the journey doesn't end there.

"After fertilization occurs the egg travels from the fallopian tube to the uterus," says Laura Goetzl, author of Healthy Pregnancy Over 35 (Dorling Kindersley Ltd, 2005). "It attaches to the lining of the uterus, and then the placenta starts to form." This contact between the egg and the uterus triggers the hormonal changes associated with pregnancy.

At this time, you have no idea you're pregnant. But inside you, the little ball of cells that will eventually develop into your baby is working hard, dividing and growing.

"The contact between the mother's blood and the fertilized egg starts the hormonal changes that lead to the symptoms of pregnancy," Goetzl says. The hormone change caused by pregnancy causes similar symptoms to the hormone change caused by an oncoming period, such as tender breasts and mood swings.

Jessica Cook, an expectant mom from San Francisco, Calif., mistook her first symptoms of pregnancy for signs that her period was coming. Her first clue was a painful orgasm during sexual intercourse. "I didn't know it was a sign of pregnancy," she says. "We just thought I had some weird ovary thing and that it was a sign that my period was coming." Cook also experienced extreme emotions, which she mistook for premenstrual syndrome.

"My first sign was a pain in my breasts," says Jennifer Matlack, a mom from Bethel, Conn. "A very deep, gnawing pain, nothing like the pain I normally get around my period."

When Janene Mascarella, a mom from Miller Place, N.Y., got pregnant with her second baby, she experienced the same food cravings she had with her first pregnancy. "[During] my first pregnancy I strangely found myself drawn to the deli department at my grocery store," she says. "My husband and I weren't officially trying to have a second baby, but we were just kind of winging it. At a dinner party, I sat down before a platter of salami and cheese and whispered to myself, 'meat.'" When her husband heard her, he knew she was pregnant again, Mascarella says.

Many women mistake the first signs of pregnancy for signs that their period is coming because in both cases, similar symptoms result from hormonal changes. "Other early signs are needing to go to the bathroom more frequently, tiredness, a more sensitive sense of smell, nausea and then obviously a missed period," Goetzl says.

Up to this point, you may have had your suspicions. Sore breasts, raging hormones, a nauseas feeling and finally a missing period all pointing to pregnancy. But until you take a pregnancy test, you can't be sure. So what triggers a positive reading on the at-home pregnancy test?

"When the fertilized egg implants in the lining of the uterus, a hormone called beta HCG, or human chorionic gonadotropin, becomes present and increases as the pregnancy continues," Goetzl says. "This is what the pregnancy test detects."

At this point, you've been pregnant for a month or so. The baby inside you is still very tiny, but it has a heartbeat, and the nervous system, stomach, lungs, liver and pancreas have started to form. That's quite a dramatic change from a sperm and an egg.

Before you even know for sure that you are pregnant, your baby is going through the most dramatic changes of his or her life. And one of the most amazing parts of being pregnant is knowing that your baby started as a sperm searching for an egg. The process of fertilization and the start of a new life is the first of many miracles of parenthood.

Want to see more?

• Pregnancy Stories: Real Women Share the Joys, Fears, Thrills and Anxieties of Pregnancy from Conception to Birth
• Am I? The Early Signs of Pregnancy
• Baby's Early Days: First Trimester Growth
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