What is a Viable Pregnancy and How is it Diagnosed?

Strict guidelines are used to ensure a correct diagnosis is made.

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A viable pregnancy is one that can potentially lead to the birth of a living baby. In other words, a pregnancy is viable if it seems to be progressing normally, there are no indicators of miscarriage, and there is a reasonable expectation that the pregnancy will result in the birth of a live infant. 

A nonviable pregnancy would be a pregnancy in which there is no chance of a live infant being born, such as an ectopic pregnancy, a molar pregnancy, or a pregnancy in which the baby no longer has a heartbeat.

What is Age of Viability?

When used to describe a fetus, or developing baby, the term viability refers to the time in pregnancy when the baby can be born and have a reasonable chance of survival. For most hospitals in the United States, the age of viability is about 24 weeks 0 days of the pregnancy.

The term "age of viability" refers to the point in pregnancy at which the baby could have a chance of survival if born prematurely, which is generally around 24 weeks of pregnancy.

When a Pregnancy or Fetus Becomes Nonviable

A nonviable pregnancy is one in which there are indications that the pregnancy is failing and a miscarriage is expected. This can be used to describe situations where an ultrasound has not found some of the structures of the developing pregnancy or fetus, such as an empty gestational sac, no fetal pole, or no fetal heartbeat. 

The Society of Radiologists in Ultrasound has developed criteria to help healthcare providers assess prenatal viability using ultrasound.

The goal is to ensure providers are not too quick to label a pregnancy nonviable and avoid treatments aimed at ending a potentially viable pregnancy.

The criteria is more stringent than in the past, and includes the following as diagnostic of a nonviable pregnancy:

  • Mean sac diameter of 25 millimeters or greater and no embryo

  • Absence of embryo with heartbeat at 2 or more weeks after a previous scan that showed a gestational sac without a yolk sac

  • Absence of an embryo with heartbeat 11 or more days after a scan that showed a gestational sac with a yolk sac.

The Society of Radiologists also highlighted eight criteria that raise suspicion of pregnancy failure (but not confirmation, so more time and investigation is required):

  • Crown–to-rump length of less than 7 millimeters and no heartbeat

  • Mean sac diameter of 16 to 24 millimeters that doesn't contain an embryo

  • Absence of embryo with heartbeat 7 to 13 days after a scan that showed a gestational sac without a yolk sac

  • Absence of embryo with heartbeat 7 to 10 days after a scan that showed a gestational sac with a yolk sac

  • Absence of embryo 6 or more weeks after last menstrual period

  • Empty amnion (amnion seen adjacent to yolk sac, with no visible embryo)

  • Enlarged yolk sac (greater than 7 millimeters)

  • Small gestational sac in relation to the size of the embryo (less than 5 millimeters difference between mean sac diameter and crown–to-rump length).

    Viability in a Pregnancy of Unknown Location

    Sometimes, a woman has an elevated hCG hormone, but there is no evidence of a pregnancy in the uterus—this is called a pregnancy of unknown location.

    That being said, in this instance, according to an article in the New England Journal of Medicine, if the hCG level is greater than 2000, there is only a small chance (about 2 percent) that the pregnancy is a viable intrauterine pregnancy. If the hCG level is greater than 3000, the chance of a viable intrauterine pregnancy is about 0.5 percent.

    Instead, it's much more likely that the pregnancy is either a nonviable intrauterine pregnancy or an ectopic pregnancy. Still, based on this small chance, your obstetrician-gynecologist may recheck your hCG level and an ultrasound in a day or two to be sure the pregnancy is indeed nonviable (assuming you are feeling well and medically stable).  

    A Word From Verywell

    The purpose of these strict guidelines is to prevent the diagnosis of a "nonviable" pregnancy that is actually viable. While it may mean a bit more waiting or even worry on your part, it is meant to ensure a 100 percent correct diagnosis.

    That being said, be sure to talk with your obstetrician-gynecologist. You play an important part in this process, and your doctor will want to consider your wishes. 

    Sources:

    American College of Obstetrics and Gynecology. (May 2015). Practice Bulletin: Early Pregnancy Loss.

    Doubilet PM et al. Diagnostic criteria for nonviable pregnancy early in the first trimester.<N Engl J Med. 2013 Oct 10;369(15):1443-51.

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