Pregnancy Information Center

Information, Symptoms, Treatments and Resources


Your First Trimester - Week 5


Week 5


What's Happening To Your Body

You’ve missed your menstrual period. For many women, this is the first sign that they're pregnant. Other women recognize symptoms of early pregnancy, such as sore breasts, fatigue, backaches, nausea and morning sickness, frequent urination and mood swings. These are all typical pregnancy symptoms during the fifth week. If your breasts are very tender and bother you while you sleep, try sleeping in a sports bra or another soft bra that provides support but doesn’t poke you.

Heartburn may start happening this week. If this is the case, consider eating smaller, more frequent meals throughout the day. You may also start to experience headaches due to a rise in hormone levels.

Be even more careful of the foods you eat. Listeriosis is just one example of foodborne illness that may make your baby susceptible to birth defects or cause you to miscarry. In order to prevent foodborne illness, be sure to stay clear of soft cheeses (like brie and feta, unless the labels say they're made from pasteurized milk), unpasteurized foods, and raw and undercooked seafood, meat and eggs. Soiled pet litter boxes may also contain traces of the rare parasitic disease toxoplasmosis, which can cause serious birth defects. As a precaution, don't clean out your cat’s litter box while pregnant; ask your partner, a friend or a neighbor to do it for you.

What's Happening To Your Baby

Your baby is the size of a sesame seed. Your baby looks more like a tadpole than a baby at this point. It's roughly the size of the tip of a pen, at around 1/20 inch long (1.3 mm), measured from the crown of the head to its bottom, also called rump. Crown to rump is the standard way to measure your baby’s length during the first 20 weeks of gestation.

This week, your baby’s heart is forming and, by the end of this week, begins to beat at a steady rhythm. Its skeleton begins to form, as do the structures that will become its eyes and ears.

Also during this week, the placenta forms. The placenta is responsible for the transfer of nutrients and oxygen from your bloodstream to the fetus. It also allows the fetus to get rid of its own waste by transferring it back to your circulatory system. It also continues to secrete the hormones progesterone and estrogen, which help keep your pregnancy steady.

Read This Next: Week 6

In Case You Missed It: Week 4

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