Thirteen weeks of pregnancy marks the official start of the second trimester, a transition often welcomed as a period of renewed energy and reduced discomfort. This stage shifts focus from foundational development to rapid growth and refinement. The chance of miscarriage drops significantly, often leading parents to share the news more widely.
Fetal Development Milestones
At 13 weeks, the developing baby is fully categorized as a fetus, having completed the most vulnerable stage of organ formation. The fetus is approximately the size of a peach or a lemon, measuring about 3 inches (7.4 cm) in length from crown to rump and weighing around 1.25 ounces (35 grams).
The head, which previously accounted for a large portion of the body, is beginning to grow more in proportion with the torso and limbs. Facial features are becoming distinctly human, with the eyes moving closer together and the ears settling into their final position.
Within the skeletal structure, the process of ossification is accelerating, replacing cartilage with true bone, especially in the long bones and skull. This provides structural support for the rapidly growing body. Internally, the liver and pancreas are starting to function, and the intestines have moved from the umbilical cord into the abdominal cavity. The fetus is actively practicing reflexes, including swallowing amniotic fluid, which the developing kidneys process and excrete as urine. Vocal cords are also beginning to form.
Maternal Physical and Symptom Changes
The transition into the second trimester often brings a noticeable improvement in overall well-being for the pregnant person. The intense nausea and persistent fatigue that characterized the first trimester subside, leading to the designation of this period as the “honeymoon phase” of pregnancy.
The uterus has grown substantially and is typically rising out of the pelvis, which may relieve the constant pressure on the bladder that caused frequent urination in earlier weeks. This growth, however, can lead to new sensations, such as round ligament pain, felt as a sharp or dull ache in the lower abdomen or groin as the supporting ligaments stretch.
Physical changes in appearance become more apparent as the uterus expands, potentially resulting in the appearance of a small baby bump. Hormonal changes are also visible on the skin, sometimes causing hyperpigmentation. This includes the darkening of the line running from the belly button to the pubic area, known as the linea nigra, and dark patches on the face called melasma. Increased blood volume and hormonal activity can also lead to heightened libido, gum sensitivity, and an increase in clear or milky vaginal discharge.
Medical Screening and Care at the Start of the Second Trimester
At 13 weeks, the focus of prenatal care shifts from confirming the pregnancy to monitoring the growth and development of the fetus. For many, this marks the end of weekly or bi-weekly appointments, with visits generally spacing out to once every four weeks until later in the pregnancy.
This week often finalizes the results of first-trimester screening tests, such as the Non-Invasive Prenatal Testing (NIPT) and the Nuchal Translucency (NT) scan. These tests, performed between 11 and 14 weeks, assess the risk of chromosomal conditions like Down syndrome, and the results inform any necessary next steps.
Healthcare providers typically use this appointment to discuss upcoming second-trimester milestones, including the detailed anatomy scan scheduled for around 18 to 22 weeks. General guidance on lifestyle adjustments is reinforced, including clearance for moderate exercise and emphasizing sound nutritional practices. Providers will also check maternal blood pressure and weight, and listen to the fetal heartbeat using a Doppler device.