Your baby continues to grow rapidly now, and his organs and systems are becoming more efficient and complex. His brain is growing larger and more sophisticated every day, enabling him to perform more functions. His skeleton is becoming harder, as calcium replaces cartilage in his bones. He is now capable of a range of movements and activities -- and he is likely to be practicing them all. Inside your womb in his 13th week, he is busy jumping, stretching, kicking, yawning, swallowing, separating his fingers -- maybe even sucking his thumb or fingers.
Your fetus looks increasingly like a baby. Now his eyes are closer together at the front of his face, and his ears are also almost in the right position. His head, which was initially large in proportion to his torso, will grow more slowly from now on, as his body grows at a more rapid rate. By the time he is born, his head will be one-quarter the size of his body.
For all this furious growth and activity, your baby is still very small, approximately three inches from crown to rump -- roughly the size of a small apple. He still only weighs about two-thirds of an ounce. From now on, there is less likelihood of his being affected by exposure to drugs or most infections. But the little person growing inside of you is still very vulnerable, so you should continue to be careful about what you do.
No amount of alcohol is considered safe during pregnancy, so it's important not to drink at all. Heavy drinking or binge drinking during pregnancy can cause permanent mental retardation in your child, and even light or social drinking has been linked to learning disabilities and a host of other problems.
And if you are a cigarette smoker and you have not stopped smoking, you need to do so. It is likely you've already heard this from friends, relatives, your health care provider -- and even from the warning on your cigarette pack: Cigarette smoking can harm your child's growth and development. It isn't too late to stop.
Smoking during pregnancy can cause a range of serious problems. It can retard fetal growth and cause subtle changes in brain development, trigger breathing problems in the newborn, and increase the risk of everything from placenta previa to Sudden Infant Death Syndrome (SIDS). Experts now conclude that smoking during pregnancy can triple the risk of SIDS -- and the more cigarettes the mother smokes, the greater the risk. Even secondhand smoke can harm your baby, doubling its odds of dying from SIDS.
If you have tried to quit smoking and failed, talk to your practitioner right away. National organizations like the American Cancer Society and the American Lung Association also offer support and resources for those who wish to quit.
Unfortunately, most of the popular aids that can help smokers give up cigarettes -- including patches, gum and pills -- are not safe during pregnancy, because they contain nicotine. The prescription drug Zyban, which has proven helpful in smoking cessation, is also not recommended for use during pregnancy. So getting support and help while quitting is even more important.
At this point in your pregnancy, you're probably too big for your regular clothes. It's time to switch to looser-fitting clothing or treat yourself to maternity clothes that will last for the duration of your pregnancy. You may also be noticing stretch marks. After you have your baby, there are many options for treating stretch marks, but for now, avoid steroid creams because you could pass the drugs on to the baby. Your breasts are likely to be larger, too. By the end of your pregnancy, your breasts may be double to quadruple their normal weight as milk ducts become ready for nursing.
Campbell, Stuart MD. Watch Me Grow! St. Martin's Press.
Curtis, Glade OB/GYN and Judith Schuler, MS. Your Pregnancy Week by Week. De Capo Press.
Pregnancy Calendar, Week 13, from the American Academy of Family Physicians.
Surgeon General's Report: Women and Smoking Fact Sheet, Tobacco Use and Reproductive Outcomes Fact Sheet, http://www.cdc.gov/tobacco/data_statistics/sgr/2001/highlights/outcomes/
Smoking: What you need to know. March of Dimes.
Hofuis, W et al. Adverse health effects of prenatal and postnatal tobacco smoke exposure on children. Archives of Diseases in Childhood, Vol. 88: 1086-1090
Nemours Foundation. Sudden Infant Death Syndrome (SIDS). http://kidshealth.org/parent/general/sleep/sids.html