The First Trimester

by Shannon Bartlett

Although no one would guess by looking at you, a miracle has begun inside you. During the first trimester, your baby grows from mere cells to tiny being who looks like a baby, with eyes, nose, mouth, arms and legs that move. Your baby's heart begins beating and other organs form.

See how your wee one changes in the week-by-week view for fetal development, or click to learn more about pregnancy at 1-4 weeks, 5 weeks, 6 weeks, 7 weeks, 8 weeks, 9 weeks, 10 weeks, 11 weeks, 12 weeks, 13 weeks or 14 weeks. If you're a member, you can customize your dates and follow along with the Pregnancy Calendar, too!

This trimester can be exciting, exhausting, thrilling and a bit scary, all rolled into one. Your body is changing, working overtime to produce hormones and build extra blood cells.

It's easy to be overwhelmed by all that's new, but take your time adjusting to the emotional and physical changes. Keep in mind you have nine months ahead to enjoy and prepare.

When Does First Trimester End?

The first trimester starts with the first day of your last menstrual period, and ends roughly 13 or 14 weeks later. Three different methods are used to divide up a pregnancy into the three trimesters. Each methods results in slightly different spans for the trimesters.

The development method uses the developmental stages to divide up a pregnancy. The second trimester begins at 12 weeks and the third at 27 weeks.

  • From LMP to 12 weeks, the embryo develops all the major organs.
  • From 12 weeks to 27 weeks the fetus continues developing . At 27 weeks, your baby is considered viable.
  • From 27 weeks on, your baby gets matures and prepares for delivery.

The gestation method divides the 40 weeks of gestation into three equal stages. Using the gestation method, the second trimester begins at 13 weeks 3 days and the third at 26 weeks 6 days.

The conception method splits the 38 weeks after conception development into the three equal trimesters. The two week before conception become part of the first trimester. With this method, the second trimester begins at 14 weeks 5 days and the third at 27 weeks 3 days.

Your Body

Pregnancy Symptoms: During early pregnancy, you'll join one of two camps. You might begin to experience early pregnancy symptoms like nausea, breast changes and fatigue or you might not be able to tell you're pregnant. Moms from each group go on to birth healthy babies.

Emotional Changes: You can blame some of your see-sawing emotions on pregnancy hormones, but there's more to these fluctuations that just body chemistry. Having a baby -- whether your first or not -- is life changing. Your wide range of feelings about the pregnancy might include joy, worry, excitement, and apprehension.

Physical Changes: When we think of a pregnant woman, we envision an expanding middle. During the first trimester, you won't see much of a bump, but you will notice growth in another area -- your breasts. They're apt to be tender and larger. One of your first pregnancy purchases might be a larger bra. From early pregnant, your breasts change and develop to produce milk.

Weight Gain: If you started your pregnancy at a normal weight, you'll probably gain somewhere around five pounds. The baby's only responsible for a few ounces. Amniotic fluid, extra blood volume and breast tissue make up the rest. Not everyone gains weight the first weeks of pregnancy. Some women actually lose due to morning sickness.

Your Baby's Development

Fertilization: About two weeks after the first day of the last menstrual period, your ovary releases an egg. It met up with a sperm in the fallopian tube. The fertilized egg has the all the chromosomes needed to determine height, hair color, sex and more. The egg begins to divide, and begins its trip toward the uterus.

Implantation: Your microscopic baby grows and doubles in size every day. Five to seven days later, it burrows into the lining of the uterus. The placenta and umbilical cord begin to form.

Week 4: You've misses your period. Your baby, called an embryo at this stage, measures about 1/100 of an inch long. He or she already has a spinal cord, and is dividing into three layers that will become the different organs and systems in the body.

Week 6: Your baby's growth rate is amazing! The embryo lengthened from 1/100 of an inch to about 1/6 inch. Tiny limb buds appear. Soon you'll be able to see legs and arms, Blood is being pumped through the fetal circulation, and a heartbeat can be seen on an ultrasound. The heart has begun beating and pumping blood. If you have a dating ultrasound, now, you'll probably be able to see a fast blip during the scan. That's your baby's heartbeat!

Second Month: At the beginning of this month, the baby is about 1/2 inch long and weighs a fraction of an ounce. By the end of the second month, all the major body organs and body systems have begun to develop. Your baby, now called a fetus, looks like a tiny human. The baby bean's now a little over an inch long and still weighs less than an ounce.

Third Month:By the end of this month, the organs and other systems are completely formed. Tiny hands, complete with fingers flail, legs kick, toes wiggle, and the mouth opens and closes. He or she is still too small for you to feel the movement. By the end of this month, the baby will be about 4 inches long and weigh just over an ounce.

Prenatal Appointments

Once you suspect (or confirm) that you're pregnant, give your health care provider a call. Most will want to see you within 12 weeks of your last normal menstrual period. If you're over 35, a high risk pregnancy or a teen, your midwife or doctor will probably schedule an earlier appointment so you can receive more intensive support. In the first trimester, you'll probably have a visit every four to six weeks, with optional ultrasounds for dating and screening.

The first prenatal appointment: The office will schedule you to come in as early as six weeks or as late as 13 weeks.

A dating ultrasound: If your cycles are irregular or you're not certain of your last menstrual period, your provider might suggest a dating ultrasound. Be sure to ask for copy of baby's first picture for your scrapbook!

The First Trimester Screening consists of an ultrasounds and a blood test. The data combines to let you know the risks that your baby has a genetic condition. If you decide to go ahead with diagnostic testing, a chorionic villi sampling can be scheduled between between 8 and 12 weeks or an amniocentesis scheduled between 15 and 21 weeks.

First trimester wrap up visit will be schedule about 4 weeks after your first prenatal visit. You'll be able to go over screening results, ask questions about symptoms, exercise, nutrition, as well learn what to expect next.

First Trimester Concerns

Bleeding: Bleeding during early pregnancy doesn't means that you will miscarriage. In fact, about half of women who have bleeding do not have miscarriages. However, bleeding is not ever normal and your midwife or doctor will want you to call. If your bleeding is heavy or accompanied by cramps, pain, fever, or weakness, medical attention should be sought immediately.

Miscarriage: About 1 in 6 pregnancies end in a miscarriage, and most of these happen within the first twelve weeks of pregnancy. Usually the cause isn't known and in most cases, nothing can be done to stop a miscarriage from happening once it has begun. If your bleeding is heavy or you're passing tissue, let your provider know.

Ectopic Pregnancy: An ectopic pregnancy occurs when the fetus develops in the fallopian tube instead of the uterus. An ectopic pregnancy can be life-threatening. The symptoms include sharp abdominal cramps or pains on one side.

Hyperemesis: gravidarum is a severe form of unrelenting nausea and vomiting in pregnancy. It results in weight loss, dehydration and sometimes electrolyte disturbance. Severe cases often require a stay in the hospital so that the mother can receive fluid and nutrition through an intravenous line.

Take advantage of the practical, thought-provoking and entertaining resources we've gathered up on early pregnancy. Whether you'd like a peek at your baby's development, wonder what's happening with your body or want to meet up with others sharing this stage of pregnancy, we have what you're looking for.