First Trimester

Both your body and developing baby will go through tremendous changes during the first trimester of your pregnancy. Your baby will grow from a zygote (fertilized egg) to an embryo to a fetus in just three months.

First Trimester Pregnancy: Hormone Changes

There are five major pregnancy hormones that are crucial to your baby growing. While these hormones are essential, they can cause unpleasant side effects like morning sickness in the first trimester and looser ligaments sometime in the middle of the second trimester right through to your due date.

Estrogen and progesterone are hormones you've probably heard plenty about. Estrogen is produced by the ovaries when you're ovulating. When you're pregnant it's produced by the placenta. Estrogen is responsible for breast enlargement, one of the early first trimester symptoms. Progesterone comes from your own blood and acts like a muscle relaxant when you're pregnant. It's important in preventing the uterus from contracting until your delivery date. It's also responsible for heartburn, acid reflux, constipation and looser ligaments.

The human placental lactogen hormone (hPL) is created by the placenta and helps your body break down nutrients for the baby. The human gonadotropic hormone (hCG) regulates progesterone production and plays a role in the gender of your baby. It doubles in values every two days during the first trimester and then plateaus. The human gonadotropic hormone is thought to be the cause of morning sickness. The final pregnancy hormone is prolactin and it's responsible for stimulating milk production.

Important Stages of the First Trimester

There is no specific stage that's more important than another during the first trimester. The entire period is important to your baby's development and your unborn child will go from the size of a pinhead to approximately nine centimeters in just 12 weeks. By the end of the first three months of your pregnancy an ultrasound will be able to tell you the gender of your baby. Your baby will be fully formed with tiny arms and legs and a beating heart. All internal organs will be formed but, like everything else, will need to mature in order for your child to be able to survive outside of your body.

You won't know you're pregnant for sure until four weeks or later into your pregnancy. This will be two weeks after ovulation. During these 14 days the cells in the fertilized egg are dividing and implantation occurs around four weeks. Some women experience first trimester cramping around this time as the blastocyst burrows itself in the lining in your uterus. Mild cramping can continue throughout the first trimester as your uterus expands and stretches to accommodate your growing baby.

Around week five the embryonic period begins. A heartbeat can be detected around week six. Your baby will start to move at around eight weeks even though you won't feel her move. By the end of the first trimester, and the beginning of the second trimester, your baby will have a human profile, the beginnings of genitals and will begin developing fingernails.

The Beginning of the Second Trimester

If a woman isn't quite sure how far along she is in her pregnancy, an ultrasound can let her know how many weeks old her developing baby is. The unborn child is examined and the fetus' physical characteristics are analyzed. Skeleton bones will become visible around 15 weeks and facial expressions are noticeable around 16 weeks. A more defined neck around week 14 can indicate the start of the second trimester.

Pregnancy Termination

Women who don't wish to be pregnant often choose to have a first trimester abortion. There are three procedures to terminate a pregnancy during this stage: Mifepristone, Methotrexate or Vacuum Aspiration. The final procedure is the most effective at 99 percent. The first option is given orally and the second option is administered by injection. All three procedures have their advantages and disadvantages.