At six weeks, some doctors perform a sonogram, also called an ultrasound, to determine the health or viability of the developing embryo. This is generally the earliest that anything is visible on an ultrasound, although at this point it will not look much like a baby, since development is still in the early stages.

At the end of your 13th week of pregnancy you are at the beginning of your second trimester. Your baby is almost 3 inches long and weighs almost an ounce, according to Baby Center. It is important to realize that not all women experience the same symptoms at the same time.

One of 60 pregnancies is ectopic, or growing outside of the uterus. Vaginal bleeding is common in early pregnancy, occurring in 20 percent to 30 percent of all pregnancies, the American Pregnancy Association says. Vaginal bleeding in ectopic pregnancy can be heavier than bleeding seen in intrauterine pregnancies.

During the first month of pregnancy, your baby-to-be grows at a rapid rate. But he's only about 1/5 of an inch long 4 weeks after conception, still not large enough to account for any weight gain by himself. Most women gain very little weight related to pregnancy itself during the first month.

Week 6 of pregnancy is considered early pregnancy and is about halfway through the first trimester. Some women find out they are pregnant around this time. Babies at this stage can be measured with an ultrasound, although many details may be difficult to see.

Progesterone is an important hormone in fertility and pregnancy and is sometimes called the hormone of pregnancy. It plays a vital role in developing and maintaining a healthy placenta and fetus, particularly during the first trimester of pregnancy.

Pregnancy is a happy time for most women. While most expectant mothers experience an average pregnancy, there are certain dangers associated with this condition which can result in health complications for both you and your baby. Knowing what these complications are can help reduce your risk of experiencing them.

At 5 months pregnant -- about 20 weeks -- you are halfway through your pregnancy and in the middle of your second trimester. Most women experience fewer pregnancy symptoms in this trimester than in the first and third trimester.

At seven months (28 weeks) into your pregnancy, you are in the first week of your third trimester and about 12 weeks from your due date. By this week, your baby weighs 2 1/4 pounds (about the size of a Chinese cabbage) and measures 14.8 inches from the top of her head to her heels, reports BabyCenter.

Scar tissue, also known as adhesions, can cause pregnancy complications when it forms in, on or around the uterus or fallopian tubes. Adhesions form as the result of trauma, such as surgery or infection.

Although many people tell children, “There’s a baby in my stomach," when they’re pregnant, they know the baby is actually growing in the uterus, the female reproductive organ.

At week 8 of pregnancy, you enter into the final third of your first trimester. During this time, the symptoms of pregnancy -- other than missing a period -- begin to emerge. Your body is working hard to nurture a new life, producing hormones to support the pregnancy.