Week 13 marks the end of the first trimester and the start of a new stage in your pregnancy. Trimester two lasts for months four, five, and six of pregnancy. You should start feeling more comfortable from this week.

You may find that the tiredness and nausea reduce or disappear for a while.

This Medical News Today Knowledge Center feature is part of a series of articles on pregnancy. Take a look at the other articles in the series:

First trimester: fertilization, implantation, week 5, week 6, week 7, week 8, week 9, week 10, week 11, week 12.

Second trimester: week 13, week 14, week 15, week 16, week 17, week 18.

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In the second semester, many women feel more comfortable.

At this stage of your pregnancy, you may continue to experience physical symptoms, such as:

In addition to fetal growth and development, your placenta is growing and now weighs approximately 1 ounce. You can expect to have a 1-2 pound placenta when the baby is born.

Be aware that pregnancy increases the risk of a urinary tract infection (UTI).

Signs to look out for include:

  • frequent, urgent, or painful urination
  • pain or cramping in the lower abdomen
  • back pain
  • cloudy, foul-smelling, or bloody urine
  • feeling unwell, achy, and tired
  • high temperature
  • shivering or chills

If you experience symptoms of a UTI or another infection speak to a doctor.

At the end of the first trimester, the hormonal levels settle down to some extent, and you will start to feel more comfortable.

Libido: Some women find that these hormones lead to an increased sex drive at this time. This is not true for everyone, however.

Cravings can occur as hormonal changes affect your senses of taste and smell. Changes in blood sugar levels can also leave you craving sugary foods.

Try to limit your sugar intake, opting instead for a variety of fruits, vegetables, and healthful savory snacks. Also, make sure your diet has adequate protein to keep your blood sugars more stable throughout the day. Most women need around 70 grams of protein each day.

Weight gain: Remember to watch your weight, too, as "eating for two" does not mean eating double, and it may be hard to shift any extra pounds after the baby is born.

You should increase your calorie intake by about 300 calories a day, keeping in mind that your weight gain in pregnancy is recommended to occur mostly in the second and third trimesters.

At around 2.5 inches in length, your baby is now about the size of a peach. The head is becoming more in balance with the rest of the body, with its size making up about one-third of its overall frame.

Your baby can move their arms and may now be able to put their thumb in their mouth.

Other developments that are underway between week 11 and week 14 include the following:

  • The salivary glands start working, and vocal cords continue to develop.
  • The eyelids close around now and will remain closed until week 28.
  • The heartbeat can now be heard with an external Doppler.
  • The lungs continue to mature, and amniotic fluid is inhaled and exhaled.
  • The spleen is working to produce red blood cells.
  • The intestines continue to migrate from umbilical cord to the abdomen.
  • The ovaries or testes are fully developed.
  • The sex organs are appearing.
  • The limbs are long and thin.
  • The head is large.
  • Tooth buds are appearing.
  • The baby can make a fist.
  • Body hair is growing.
  • Muscles and the nervous system are maturing.
  • The kidneys are producing urine, which becomes the baby's amniotic fluid.

The baby now has either a penis or clitoris growing between the legs, but these are too small for an ultrasound scan to distinguish yet.

From weeks 11 to 14, you may have an ultrasound to evaluate nuchal translucency. The scan can check whether there is additional fluid under the skin behind the baby's neck.

This is important in testing for some medical conditions that may affect your baby, such as Down syndrome.

Blood tests are also used to screen for Down syndrome, Trisomy 18, spina bifida, and other problems.

Sequential screen or integrated screen: These blood tests are done between weeks 10 and 13 and can be repeated during weeks 15 to 20. They test for fetal proteins that may indicate the presence of Down syndrome or other chromosomal issues. The proteins evaluated include Pregnancy-associated plasma protein screening (PAPP-A) and Human chorionic gonadotrophin (hCG).

There are also blood tests available which look at your baby's DNA, which is present in your blood stream late in the first trimester. These tests can also provide information on your baby's risk for chromosomal abnormalities.

Other tests may be carried out later in pregnancy to confirm the blood test results, such as amniocentesis or chorionic villus sampling (CVS).

Be sure and discuss all options for genetic screening with your doctor to see which option if best for you, if you choose to do any screening at all.

If you have been feeling queasy so far, this week may mark the beginning of a more comfortable stage.

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Healthful options will benefit both you and your baby.

During the next few weeks, your pregnancy will begin to show. The second trimester is a good time to take a trip or a holiday, as you will be feeling better.

Maintain this feeling of wellbeing by following a healthful lifestyle, with a well-balanced diet and suitable exercise.

As time goes on, your baby will also be less at risk from infections and other hazards that you may be exposed to. However, the risks remain, and you should continue to be watchful and avoid alcohol, tobacco, fish that are high in mercury, and large amounts of caffeine.

Call your doctor if you are experiencing symptoms of an ectopic pregnancy or miscarriage such as vaginal bleeding or passage of tissue, leaking vaginal fluid, feeling faint or dizzy, low blood pressure, rectal pressure, shoulder pain, or severe pelvic pain or cramping.