The fundus is the dome-shaped top portion of the uterus, which plays a significant role in both carrying a pregnancy and recovering afterward. Monitoring the position and texture of this muscular organ is a fundamental way medical providers track the progress of a pregnancy. Its changing location provides a measurable indicator of fetal growth, while its ability to contract and firm up is a measure of uterine health.
Locating the Fundus During Pregnancy
The location of the fundus changes dramatically as the uterus expands to accommodate the growing fetus. Early in pregnancy, the entire uterus remains contained within the bony structure of the pelvis. It is not generally palpable above the pubic bone until approximately the twelfth week of gestation.
By the twentieth week, the fundus has typically risen to the level of the umbilicus. This milestone is often used as a midpoint reference for the pregnancy. Medical providers use this landmark to begin measuring the distance from the pubic bone to the top of the fundus, a process known as fundal height measurement.
The fundal height measurement provides an estimate of fetal size and growth rate, with the measurement in centimeters generally corresponding to the number of weeks of gestation after 24 weeks. Around 36 weeks, the fundus reaches its highest point, often touching the bottom of the breastbone. Later in the final weeks, the fundus may slightly drop as the baby descends deeper into the pelvis in preparation for labor, a process referred to as “lightening”.
What the Fundus Feels Like During Gestation
During the first half of pregnancy, the feeling of the fundus is generally one of deep, internal stretching and pressure as the organ expands. The feeling of tightness or firmness becomes more apparent in the second and third trimesters. This firmness is the most notable sensation related to the fundus during gestation.
The fundus will temporarily harden and tighten during Braxton Hicks contractions, which are the uterus’s practice contractions. These contractions are typically irregular and do not cause cervical change, but they can make the abdomen feel very firm to the touch for a short period. As the pregnancy advances, a person may also feel upward pressure beneath the ribs as the fundus reaches its maximum height.
The immense growth of the uterus also causes the surrounding ligaments to stretch, which contributes to the internal sensations experienced. The pressure of the enlarged uterus on other organs, such as the stomach and diaphragm, can cause discomforts, like shortness of breath and indigestion. The fundus itself, when not contracting, can be felt as a large, firm mass in the abdomen.
The Postpartum Process of Involution
After the baby is delivered, the body initiates a rapid process known as involution, the shrinking of the uterus back toward its non-pregnant size. Immediately following the delivery of the placenta, the fundus is usually located near the level of the umbilicus, similar to its position at 20 weeks of gestation. This immediate contraction closes off the blood vessels at the site where the placenta was attached, preventing excessive bleeding.
The descent of the fundus is rapid over the next few days, shrinking at a rate of approximately one centimeter every 24 hours. By about one week postpartum, the fundus is typically located halfway between the umbilicus and the pubic bone. It is no longer palpable abdominally after about ten to fourteen days, as it has returned to the protected space of the pelvis.
The shrinking process is accompanied by uterine contractions, which the person experiences as postpartum cramping, commonly called afterpains. These cramps can feel similar to intense menstrual pain and are often more pronounced in people who have given birth before or while breastfeeding, as the hormone oxytocin is released, which stimulates uterine muscle contraction. When a person or a provider palpates the abdomen in the postpartum period, the fundus should feel hard and firm, indicating that the uterus is contracting effectively.
Recognizing Signs of Trouble
The firmness of the fundus after birth is a direct measure of its ability to contract and control bleeding. If the fundus feels soft or “boggy” when palpated, it indicates that the uterus is not contracting adequately, a condition called uterine atony. This lack of contraction is the most frequent cause of postpartum hemorrhage and requires immediate medical attention, often starting with fundal massage to stimulate contraction.
During pregnancy, an abnormal fundal height measurement may signal an issue. If the fundus is larger than expected for the gestational age, it could indicate conditions such as excessive amniotic fluid or a multiple gestation pregnancy. Conversely, a fundus that is smaller than expected may suggest slower fetal growth or low amniotic fluid levels.
After delivery, a sudden rise in the fundus above the umbilicus, especially when accompanied by a soft texture, can indicate a buildup of blood clots inside the uterine cavity. Any severe, localized pain that is not relieved by typical comfort measures or is unrelated to the expected postpartum cramping should prompt contact with a healthcare provider.