Earlier, a baby was considered full term once the mother reached the 37th or 38th week mark. However, according to the findings of American Congress of Obstetricians and Gynecologists (ACOG), babies born between the 39th and 40th weeks do much better than those born during the weeks 37 and 38 . The study also shows that fetal mortality risks are somewhat higher before the 39th week. Due to these reasons, a pregnancy is considered full term only after it reaches week 39 and is considered early term during week 38 .
The brain and nervous system development continues within the womb as the former has now taken charge of regulating bodily functions like circulation, breathing and digestion .
All the major organs are now fully mature, ready to take over their respective jobs once your baby is born . The only organ still requiring a bit of fine tuning are the lungs; they will start functioning only after birth since there is no air in the womb to practice breathing in and out . In the meantime, the lungs continue to produce large amounts of surfactant, the chemical substance that keeps the air sacs from sticking with each other once your baby starts breathing air .
The digestive system is already active, producing the sticky, greenish substance meconium that will be your baby’s first bowel movement. It contains the lanugo hair and vernix caseosa shed by your baby in this last stage of pregnancy and then swallowed along with the amniotic fluid .
Your baby is still growing the fat layer that will help control his body temperature once he comes out of the womb . His skin tone is getting closer to the color he will be at birth 
It might be a little tricky to decide the baby’s eye color immediately after birth as the irises of newborn babies often gain more pigment during the initial months of life . It means gray or light blue eyes may turn green or brown due to the additional pigment over a few months after birth. However, the eye color never turns lighter as the pigment can only increase, with brown, green and hazel eyes having more pigment compared to blue and gray eyes.
By the 38th week, your baby is about 19.6 inches (49.78 cm) long , weighing around 7 pounds (3.17 kg), almost as big as a leek . Despite the continued fat development, he is gaining less weight now as he is reaching his birth size .
Your baby is now already in position for his travel down the birth canal while his head has probably engaged in the pelvis. However in some cases, the baby may fail to turn, remaining in a feet down (breech) position in the last stage of the third trimester. Your doctor might recommend an external cephalic version (ECV) to turn a breech or transverse baby by applying external pressure on certain points of your abdomen . ECV has around 50% success rate, depending on factors like the fetal weight, maternal age and the degree of breech. Babies who remain in a breech position are delivered through cesarean section.
One of the positive things occurring in these last weeks is the indigestion and heartburn going away due to the baby dropping lower in your abdomen. It also allows more space for the lungs to stretch, relieving the symptoms of chest pain and shortness of breath. However at the same time, pressure on the bladder doubles, requiring you to use the bathroom even more often and sometimes even causing to leak urine when sneezing or laughing .
Your weight gain starts to slow down gradually around the 37th-38th weeks . Some women continue to notice their breasts leaking a thick, yellowish substance called colostrum. It is the first breast milk produced by the body and is fortified with nutrients to enable the newborn baby fight various disease and infections during the initial weeks .
Your body also starts preparing for labor as the vagina starts dilating (opening) and effacing (thinning) so the baby can pass through the birth canal .
Less than 50% of twin pregnancies reach the 38th week as most twin babies are delivered in week 37. So, make sure to keep your hospital bag ready as the labor may start any day. Doctors recommend a hospital birth for twins so specialized physicians can be ready to provide any support and care the preterm babies may need immediately after delivery . Although multiple pregnancies are associated with higher risks of complications, twins born at 38 weeks do quite well after spending around a week at the neonatal care unit.
The 38th week prenatal check up is likely to be your last one before the baby comes, unless your pregnancy goes post term (continues after the 40th week). It is advisable to consult your doctor and find out as much as possible about labor, delivery and pain medications that can help during labor .
Ultrasound scans are not usually performed in the final weeks unless your doctor needs to check the baby’s position or an ECV is required to turn him in the womb.
Your doctor will also perform a physical examination to check whether the vagina has started to open. You will be ready for giving birth at 10 cm dilation and 100% effacement . In a first time pregnancy, the dilation and effacement is likely to begin several weeks prior to the start of labor. However, they do not begin until immediately before labor in second or consecutive pregnancies.
The labor can start anytime between weeks 38 and 42 ; so, it is recommended to look out for the following signs of labor:
Published on October 11th 2014 by Pregmed Editorial Team.
Article was last reviewed on 11th October 2014.