The fifth month of pregnancy, typically spanning weeks 17 through 20 or 21, marks the midpoint and is often considered the most comfortable period of the second trimester. Early pregnancy symptoms, such as morning sickness and extreme fatigue, have generally subsided, leading to a notable increase in energy levels. This phase is characterized by substantial growth for the fetus and major physical transitions for the mother.
Fetal Growth and Key Milestones
The fetus undergoes a rapid growth phase this month, often progressing from about five inches and five ounces to roughly ten inches long and weighing one pound by the end of week 20. This growth spurt is accompanied by the beginning of fat accumulation, necessary for heat production and metabolism after birth. The skin, which remains thin, begins to produce vernix caseosa, a protective, greasy substance. This thick, whitish coating shields the delicate skin from constant exposure to amniotic fluid. Simultaneously, a fine, downy hair known as lanugo starts to cover the body, helping to hold the vernix in place.
Sensory development accelerates significantly as the ears reach their final shape and position on the head. The fetus can now actively hear sounds from the external world, including the mother’s voice, heartbeat, and digestive noises. Motor skills are becoming more refined, with the fetus practicing essential movements like sucking, swallowing, and making various facial expressions.
The most anticipated milestone is the onset of “quickening,” the first distinct sensation of fetal movement. These initial movements often feel like gentle flutters or slight nudges within the abdomen, typically beginning around 18 to 20 weeks. The practice of sucking the thumb also becomes common now, demonstrating the establishment of the sucking reflex in preparation for feeding.
Changes in the Mother’s Body
The uterus has expanded considerably, now reaching approximately the level of the navel, making the pregnancy visibly apparent and requiring a shift to maternity wear. This physical expansion causes the mother’s center of gravity to move forward, often leading to a noticeable sway in posture. This change in weight distribution can result in mild lower backaches and pelvic discomfort.
Hormonal changes, particularly the presence of relaxin, contribute to discomfort by loosening the joints and ligaments throughout the body in preparation for childbirth. The mother’s circulatory system is working harder, with blood volume increasing significantly to support the growing fetus and placenta. This shift in circulation can sometimes cause temporary drops in blood pressure, which may lead to occasional feelings of lightheadedness or dizziness.
Many experience a substantial boost in appetite during this period due to the increased caloric demand of the growing pregnancy. Skin changes are also common, including the potential appearance of the linea nigra, a dark line running down the center of the abdomen. Increased blood flow to the skin can give some individuals the characteristic “pregnancy glow,” while others may notice increased nasal congestion due to the swelling of mucous membranes.
Physiological adaptations also include an increase in heart rate to pump the larger volume of blood. Some may notice swelling in the ankles and feet, or edema, due to fluid retention and the pressure the growing uterus places on the veins. Maintaining consistent hydration and elevating the feet can help manage this common symptom.
Important Medical Screenings and Appointments
The monthly prenatal appointment during the fifth month includes routine checks essential for monitoring the health of both the mother and the fetus. Standard procedures include measuring maternal weight gain, checking blood pressure, and testing a urine sample for protein and glucose levels. These routine checks help screen for conditions like preeclampsia and gestational diabetes.
The most significant medical event this month is the comprehensive mid-pregnancy ultrasound, often called the anatomy scan or Level 2 ultrasound, which is typically performed between 18 and 21 weeks. The primary purpose of this detailed scan is a thorough examination of the fetal anatomy to ensure all major organs are developing as expected. Technicians meticulously check the fetal heart, brain, spine, kidneys, and limbs for structural development.
The scan also provides essential information about the pregnancy environment, specifically assessing the location of the placenta and the amount of amniotic fluid surrounding the fetus. Satisfactory growth is confirmed by taking various fetal measurements, which are compared against standard growth curves. If desired, this scan is also the most accurate time to determine the sex of the fetus based on the development of the external genitalia.
Discussions during this appointment will often include planning for the Glucose Tolerance Test (GTT), which screens for gestational diabetes. While the GTT is generally performed early in the sixth month, the conversation about scheduling and preparation often begins now. This proactive discussion ensures the mother is ready for this important screening.