Week 18 Update

How your baby's growing: Head to bottom, your baby is approximately 5 1/2 inches long (about the length of a large sweet potato) and she weighs almost 7 ounces. She's busy flexing her arms and legs — movements that you'll likely start noticing more and more. Her blood vessels are visible through her thin skin and her ears are now in position and stand out from her head. Myelin (a protective covering) is beginning to form around her nerves, a process that will continue for a year after she's born. If you're having a girl, her uterus and Fallopian tubes are formed and in place. If your baby is a boy, his genitals are noticeable, though he may hide them from you during an ultrasound.

How your life's changing: Bigger, more comfortable clothes are a must now as your appetite and waistline increase. Look for specially designed maternity clothes that can accommodate your expanding belly.

You may have heard that it's best to lie on your left side during your last two trimesters. Here's why: When you lie on your back, your uterus can compress your pelvic veins — in particular, the inferior vena cava, the vein that returns blood from the lower half of your body back to your heart. Lying on your left side helps remove this pressure. Try placing a pillow behind you, or under your hip or leg for comfort.

Your cardiovascular system is undergoing dramatic changes, and during your second trimester your blood pressure is probably lower than usual. Don't spring up too fast from a lying or sitting position or you might feel a little dizzy.

If you haven't already, you'll probably have an ultrasound done sometime this trimester (usually between 16 and 20 weeks). This painless procedure helps your practitioner check how your baby's growing, screen for certain birth defects, check the placenta and umbilical cord, determine whether the due date you're working with is accurate, and see how many babies you're carrying. During the exam, you might see your baby moving around or sucking her thumb. Bring your partner along, and be sure to ask for a printout for your baby's first photo album!