10 weeks

How your baby's growing:

Though he's barely the size of a kumquat — a little over an inch or so long, crown to bottom — and weighs less than a quarter of an ounce, your baby has now completed the most critical portion of his development. This is the beginning of the so-called fetal period, a time when the tissues and organs in his body rapidly grow and mature.

He's swallowing fluid and kicking up a storm. Vital organs — including his kidneys, intestines, brain, and liver (now making red blood cells in place of the disappearing yolk sac) — are in place and starting to function, though they'll continue to develop throughout your pregnancy.

If you could take a peek inside your womb, you'd spot minute details, like tiny nails forming on fingers and toes (no more webbing) and peach-fuzz hair beginning to grow on tender skin.

In other developments: Your baby's limbs can bend now. His hands are flexed at the wrist and meet over his heart, and his feet may be long enough to meet in front of his body. The outline of his spine is clearly visible through translucent skin, and spinal nerves are beginning to stretch out from his spinal cord. Your baby's forehead temporarily bulges with his developing brain and sits very high on his head, which measures half the length of his body. From crown to rump, he's about 1 1/4 inches long. In the coming weeks, your baby will again double in size — to nearly 3 inches.

At your next prenatal visit, you may be able to hear your baby's rapid heartbeat with the help of a Doppler stethoscope, a handheld ultrasound device that your practitioner places on your belly. Many women say that the beating of their baby's tiny heart sounded like the thunder of galloping horses and hearing it for the first time was very moving.

Before you got pregnant, your uterus was the size of a small pear. By this week, it's as big as a grapefruit. You may or may not be ready for maternity wear now. Even if you're not there yet, your regular clothes are probably feeling uncomfortably tight and your blossoming breasts are straining the seams of your bra. The thickening in your midsection is most likely due to slight weight gain and bloating. If you're between regular and maternity clothes, pants and skirts with forgiving elastic waistbands (or low-rise waistlines that sit below your belly) will provide some much-needed comfort.

Depending on your level of fitness, you can most likely participate in a wide range of activities during pregnancy. Swimming and walking are excellent choices for the whole nine months. Exercise promotes muscle tone, strength, and endurance — three qualities that can help you carry the weight you gain during pregnancy, prepare you for the physical stress of labor, and make it easier to get back into shape after your baby is born. (Unfortunately, there's no evidence that regular exercise shortens labor.)