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What is a single baby pregnancy called?

A single baby pregnancy, medically known as a singleton pregnancy, is a pregnancy with only one fetus (baby). This is the most common type of pregnancy, occurring in over 95% of all pregnancies. In this article, we will go over what defines a singleton pregnancy, how common they are, potential risks and complications, and what to expect during a singleton pregnancy.

Definition of a Singleton Pregnancy

A singleton pregnancy refers to a pregnancy involving only one fetus. This is in contrast to a multiple pregnancy, which involves more than one fetus. The medical term for a singleton pregnancy is “singleton gestation”.

During conception, a woman typically releases one egg that is fertilized by one sperm. This results in just one embryo implanting and developing in the uterus. With a singleton pregnancy, there is only one placenta, amniotic sac, and umbilical cord supporting the growth and development of the single fetus.

Having one fetus allows the woman’s body to devote all its resources to that pregnancy. The fetus has ample room to grow and move around in the uterus.

How Common Are Singleton Pregnancies?

Singleton pregnancies are the most common pregnancy type, accounting for over 95% of all pregnancies. According to the Centers for Disease Control and Prevention (CDC), the singleton birth rate in the United States is around 97% of all births.

While multiple pregnancies have become more common with the rise of fertility treatments and maternal age, singleton pregnancies still greatly outnumber multiple ones. Some key statistics on singleton pregnancy rates include:

  • Around 135,336 twin births occur in the U.S. each year compared to over 3.7 million singleton births.
  • Triplets or higher order multiples only make up 2% of all multiple births.
  • Younger women are more likely to conceive singletons while multiple pregnancy rates increase with maternal age.
  • Fertility treatments raise the odds of multiples but most assisted reproductive technology (ART) pregnancies are still singletons.

Singleton pregnancy rates also vary by geographical location. Developing countries tend to have higher percentages of singleton births compared to developed countries. Access to fertility treatments is more limited which keeps multiple pregnancy rates lower.

Risks and Complications

Singleton pregnancies are lower risk overall compared to multiple pregnancies and births. However, there are still some potential complications to be aware of.

Risks During Pregnancy

  • Miscarriage – Risk of miscarriage is around 10-15% for singleton pregnancies.
  • Preeclampsia – A serious condition involving high blood pressure that affects around 5-8% of pregnancies.
  • Gestational diabetes – Glucose intolerance and high blood sugar affecting 2-10% of expectant mothers.
  • Placental abruption – Premature separation of the placenta from the uterine wall.
  • Intrauterine growth restriction (IUGR) – Poor growth of the fetus during pregnancy.

Risks During Labor and Delivery

  • Preterm birth – Singleton babies born before 37 weeks of pregnancy.
  • Birth injuries – Injuries to the baby during the birthing process, such as broken collar bones.
  • Cord prolapse – When the umbilical cord slips through the cervix before the baby, cutting off blood flow.
  • Need for cesarean delivery – Around 31% of singleton births in the U.S. are via c-section.

Risks for the Baby

  • Birth defects – Around 3% of babies are born with major birth defects.
  • Low birthweight – Singleton babies weighing under 5 pounds, 8 ounces at birth.
  • Jaundice – Yellowing of the skin and eyes, affecting over 50% of newborns.
  • Respiratory problems – Such as transient tachypnea of the newborn (TTN).

While rare in singleton pregnancies, complications like premature birth, growth restriction, and birth defects are more common in multiples. Singleton babies have lower risks for long-term health and developmental problems as well.

What to Expect During a Singleton Pregnancy

Here is an overview of what to expect during the three trimesters of a typical singleton pregnancy:

First Trimester (Weeks 1-13)

  • Nausea, vomiting, fatigue
  • Frequent urination, food aversions
  • Mood swings, tender breasts
  • Baby begins developing major organs
  • Heartbeat can be detected by week 6 or 7
  • Hormone levels increase, including hCG
  • Uterus and placenta continue growing

Second Trimester (Weeks 14-27)

  • Nausea and fatigue improve
  • Fetal movements can be felt by week 16 (quickening)
  • Baby’s bones fully form, fetus puts on more weight
  • Anatomy scan around week 20 to check baby’s growth
  • Glucose screening test for gestational diabetes
  • Skin may develop stretch marks, linea negra
  • Backaches, ankle swelling, leg cramps are common

Third Trimester (Weeks 28-40)

  • More fetal activity as baby has less room to move about
  • Increased discharge, urinary incontinence
  • Shortness of breath, heartburn, constipation
  • Colostrum may leak from breasts
  • Baby descends lower into pelvis (lightening)
  • Increased blood flow leading to flushed skin
  • Braxton Hicks contractions may begin

While each pregnancy is unique, these are some standard changes a woman can expect with a typical low-risk singleton pregnancy. Proper prenatal care and remaining healthy can help reduce complications and risks during pregnancy and delivery.


In summary, a singleton pregnancy involves one fetus growing in the uterus after being conceived from one egg and one sperm. It is by far the most common type of pregnancy, accounting for over 95% of all pregnancies. While not completely risk-free, singleton pregnancies have lower risks of complications compared to multiple ones. During the three trimesters, women undergo many physical and hormonal changes as the baby develops. With proper prenatal care and precautions, most singleton pregnancies result in the safe delivery of one healthy full-term baby.