The uterus is a muscular, pear-shaped organ located in the pelvis, serving as the primary site of reproduction. It manages the menstrual cycle and supports fetal development when fertilization occurs. The uppermost portion plays a dynamic role in reproductive health and gestation. This specific area is known as the uterine fundus.
Defining the Uterine Fundus
The uterine fundus is the dome-shaped, superior part of the uterus, positioned above the points where the fallopian tubes enter the organ. This anatomical placement means the fundus is the farthest point from the cervix, the opening to the vagina.
The wall of the fundus is composed of three layers, with the thickest being the middle layer, the myometrium, which consists of smooth muscle tissue. This muscular layer gives the fundus its strength and elasticity, allowing it to perform its major functional roles. The fundus is typically inclined slightly forward, and its exact location can vary depending on factors like age and whether a person has previously given birth.
The Fundus and Pregnancy
During gestation, the fundus transforms into the largest and most dynamic part of the expanding uterus. It is the primary region that undergoes massive growth to accommodate the developing fetus, placenta, and amniotic fluid. The muscle cells in the myometrium undergo both hypertrophy (increase in size) and hyperplasia (increase in number).
The fundus is crucial during labor through a physiological mechanism known as fundal dominance. Contractions begin in the fundus, where they are the strongest and most intense before spreading downward across the uterus. This powerful contraction of the thick muscle fibers exerts the necessary downward pressure to push the fetus toward the cervix, facilitating effacement and dilation.
Clinical Monitoring: Understanding Fundal Height
The location of the fundus becomes an important diagnostic tool in prenatal care, used to assess fetal growth and verify gestational age. Healthcare providers routinely measure “fundal height,” which is the distance in centimeters from the top of the pubic bone to the highest point of the uterine fundus. This measurement is started around the 20th week of pregnancy and is taken at nearly every subsequent prenatal visit.
After about 20 weeks, the fundal height in centimeters should correspond closely to the number of weeks of gestation, typically within a range of two to three centimeters. For example, at 28 weeks pregnant, a fundal height of 26 to 30 centimeters is expected. This non-invasive measurement provides a quick screening method to monitor the pregnancy.
A fundal height measurement that is significantly smaller or larger than expected may prompt further investigation, such as an ultrasound. A larger measurement could suggest a miscalculation of the due date, multiple fetuses, or an excess of amniotic fluid (polyhydramnios). Conversely, a smaller measurement might indicate slower fetal growth (fetal growth restriction) or too little amniotic fluid (oligohydramnios).