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Intrauterine Pregnancy (IUP) Medically Reviewed

Last Updated: June 3, 2020

Definition - What does Intrauterine Pregnancy (IUP) mean?

An intrauterine pregnancy (IUP) occurs when a fertilized egg implants and starts to develop within the uterus, where it is supposed to be. The uterus is the only place where a pregnancy can develop and progress to full term.

An ultrasound finding of an intrauterine pregnancy means that the pregnancy is developing in the proper location.

Pregnancies that develop elsewhere within the female reproductive tract (cervix, ovary, fallopian tubes) are known as ectopic pregnancies are not viable, meaning they will not result in the birth of a child.

Possible concerning symptoms in early pregnancy including abdominal or pelvic pain and vaginal bleeding should be investigated to determine the location of the pregnancy and rule out any complications.

FertilitySmarts explains Intrauterine Pregnancy (IUP)

With spontaneous conception, once an egg is fertilized it continues traveling down the fallopian tube propelled by little finger-like projections called fimbriae towards the uterus where it is likely to implant in the uterine lining.

The uterus is designed specifically to house a growing pregnancy. It has a sufficient blood supply to nourish a pregnancy and the capacity and flexibility to enlarge with the growing fetus.

In some situations, the fertilized egg becomes implanted in places other than the uterus and this is known as an extrauterine or ectopic pregnancy. The fallopian tube is the most common ectopic site and the tubes are not designed to expand or grow or otherwise house a pregnancy.

Intrauterine Pregnancy DiagramA fertilized egg is designed to be naturally invasive. It has a developmental timeline that is triggered regardless of location. If there is a delay or inability of the fimbriae to move a fertilized egg out of the tube, the process of implantation can start in the incorrect location.

As the embryo grows and tries to form a placenta, there is inadequate space and the tube does not have the ability to expand which can cause the tube to burst. This rupture can cause abdominal pain with bleeding and requires immediate medical attention as it can be life-threatening.

How is an IUP confirmed?

The location of a pregnancy can be determined with an ultrasound scan. An intrauterine pregnancy can be confirmed by:

A Visible Yolk Sac

A yolk sac can be visible around 5.5 weeks gestational age with a transvaginal ultrasound. The yolk sac provides nutritional support for the developing embryo until the placenta is formed. It is the only element that can confirm a live intrauterine pregnancy until an embryo can be visualized.

An Embryo With Fetal Heart Activity

Fetal heart activity can be detected as early as 6 weeks gestation. A typical heart rate is 100-120 beats per minute (BPM) and increases over the following weeks.

  • Before 6.3 weeks a rate below 80 bpm carries a poor prognosis with an increased risk of miscarriage during the first trimester.
  • Between 6.3-7 weeks 120 bpm has a poor prognosis while under 100bpm is considered to be especially poor and at an increased risk of miscarriage.

IUP Ultrasound Diagnosis

The following terms may be used to further describe an intrauterine pregnancy.

  • A live intrauterine pregnancy is when a gestational sac contains either a yolk sac or an embryo/fetal pole with fetal heart activity and is located in the uterus. At this stage, this is a normally developing pregnancy.

  • A single live intrauterine pregnancy when a scan has located a single gestational sac that contains either a single yolk sac or a single fetal pole with fetal heart activity and is located in the uterus. At this stage, this is a normally developing pregnancy with one fetus.

  • An early intrauterine pregnancy when a scan has located a gestational sac in the uterus, but it is too early to see the embryo or fetal heart activity. More information (likely another ultrasound scan) is needed to understand if the pregnancy is progressing normally.

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