You are now entering a vital part of your second trimester as you move into the 18th week. Most of the important tests and scans required in the second trimester are performed between the 18th and 22nd weeks. So, consult your doctor regarding the exams and screening necessary for evaluating the growth of your baby.
The large intestine moves toward the back wall of the abdomen while different digestive glands begin to form . This is also the week when the uterus moves into its final position along with the fallopian tubes in a female fetus .
This week is crucial for the development of the nervous system as the tiny nerves are now covered with a protective layer (the myelin sheath), which helps massages to travel faster between nerve cells . The myelin sheath will continue to develop throughout the pregnancy and for one year after your baby is born . The nerves also start forming complex connections while the brain further specializes in sending out signals for the senses of hearing, touch, smell, sight and taste .
A thin, transparent membrane separates the two fetuses in a twin pregnancy. According to many researches, twin fetuses can sense each other at this early stage despite their sealed eyelids and lack of vision .
Your baby is around 5.6 inches (14.22 cm) long , weighing almost 7 ounces (198.4 gm), about the size of a sweet potato.
You may recognize your baby’s movements for the first time this week, if you mistook those little flutters (quickening) earlier for something like butterflies or gas . Most first time mothers feel those most awaited punches and kicks between the 17th and 24th weeks while those with subsequent pregnancies often recognize them earlier .
At week 18, your baby bump is likely to be evident enough for attracting pregnancy health tips from all quarter, be it your friends, relatives and even total strangers. You are probably gaining some weight as well. Making healthy food choices is important at this stage as the required weight gain in the second trimester is only 12 lbs to 19 lbs  (even less for overweight women). The major changes in your cardiovascular system in the second trimester are responsible for causing your blood pressure to be lower than normal . In addition to these, the hormone relaxin continues to relax the joints and muscles in your abdomen and pelvic area, leading to aches and pains in the region .
A detailed ultrasound is offered at this stage for assessing the health and development of your baby. Referred to as the fetal morphology scan, it helps your doctor to detect any structural anomalies and any breach in the placental position . Your baby is now large enough to be detected by a transabdominal ultrasound which is used for evaluating and measuring the fetal head, abdomen, spine, femur and the limbs . The gender of your baby can also be detected on the ultrasound image.
Another major change is that your doctor can now listen to the fetal heartbeat with a regular stethoscope , so a fetal Doppler is no longer necessary.
Alpha-Fetoprotein Test (AFP) or Maternal Serum Alpha-Fetoprotein Screening (MSAFP) might be recommended if you have not already had this test in the 16th-17th week. It measures the alpha-fetoprotein levels in your blood to assess the chances of your baby having certain genetic disorders. An abnormal AFP result calls for the triple screen test .
Published on June 28th 2014 by Pregmed Editorial Team.
Article was last reviewed on 13th August 2014.