A singleton pregnancy is the most common form of human gestation, involving the development of a single fetus within the uterus. This type of pregnancy is considered the biological standard against which all other gestations are measured. Understanding the nature of a singleton pregnancy helps define the expected timeline, standard medical care, and typical outcomes for the vast majority of births.
Defining the Singleton Pregnancy
A singleton pregnancy is medically defined as one where the woman is carrying only one fetus. This outcome results from a single egg being fertilized by a single sperm, forming a zygote that develops into a single embryo. Singletons represent the overwhelming majority of births, with over 95% of all live births being singleton deliveries. The entire gestational period is dedicated to supporting the growth and development of this one individual. This singular focus allows for a predictable growth trajectory and a relatively lower risk profile compared to pregnancies supporting more than one baby.
Routine Care and Monitoring
The monitoring schedule for a healthy singleton pregnancy follows a standard, predictable pattern. Prenatal appointments are typically scheduled every four weeks until 28 weeks of gestation. This frequency increases to every two weeks until 36 weeks, followed by weekly visits until delivery. Routine tests are performed during these visits. Blood pressure and weight checks are performed at every appointment, and the healthcare provider listens for the baby’s heart sounds using a Doppler device. The second trimester includes the 20-week scan, a detailed ultrasound examination to check the fetal structure and organ development. Around 24 to 28 weeks, a glucose tolerance test is routinely performed to screen for gestational diabetes. Throughout the pregnancy, the provider monitors the growth curve of the fetus, often by measuring the fundal height, to confirm the baby is tracking within the expected range.
Comparing Singletons to Multiple Gestations
The biological distinctions between a singleton and a multiple gestation are significant, particularly concerning the length of the pregnancy and the delivery process. Singleton pregnancies generally carry to term, typically 40 weeks, and have a much lower incidence of prematurity. In contrast, multiple gestations, such as twins, are often delivered earlier, with the average twin pregnancy lasting approximately 37 weeks.
This difference in gestational length contributes directly to differences in birth weight. Singletons exhibit a much lower risk of low birth weight, defined as less than 2,500 grams, compared to infants from multiple births. The rate of low birth weight can be up to nine times higher in twin deliveries than in singleton deliveries.
The delivery method also differs considerably. While many singleton pregnancies result in a vaginal birth, the risk of needing a cesarean delivery is substantially higher for multiple gestations. Data indicates that the odds of a cesarean section can be more than three times greater for a twin pregnancy compared to a singleton.