Understanding Unicornuate Uterus: Key Facts

The unicornuate uterus has several variations and therefore differing complications.

When a foetus is developing, the two sides of the body fuse together, with the specific ducts being the müllerian ducts in girls. These are classified as müllerian duct anomalies, and these can affect uterus size, shape, endometriosis, and ectopic pregnancies.

Incidence of müllerian duct anomalies

It isn’t known precisely why these abnormalities occur, since problems usually come to light after investigations for fertility or during scans of a pregnancy.

Overall incidence in women with normal reproductive outcomes – 3.2 per cent
Women with recurrent first-trimester miscarriages – 5-10 per cent
Women with late first- and early second-trimester miscarriages – 25 per cent
The unicornuate uterus applies to about 20 per cent of all müllerian duct anomalies

Symptoms of a unicornuate uterus

Most müllerian duct anomalies are asymptomatic until the first menstrual period (menarche) or at pregnancy during incidental investigations.
Repeated miscarriages are common
Unexplained infertility
Dysmenorrhea (painful periods)
Gynaecological problems
Late onset of menarche (first menstrual bleed)
Chronic pelvic pain
Collection of blood in the uterus (hematometra, hematocolpos, cryptomenorrhea) or fallopian tubes (hematosalpinx)
Endometriosis
First- and second-trimester miscarriages (spontaneous abortion)
Preterm delivery
Death of a foetus in utero
Ectopic pregnancies
If the non-communicating rudimentary horn develops a viable pregnancy, it can rupture, causing life-threatening bleeding
Stillbirth
Adenomyosis
Primary amenorrhoea (periods don’t commence)

Diagnosis of a unicornuate uterus

Physical examination isn’t very reliable unless a divided uterus is felt, or there is a clear deviation to one side of the pelvis.

How the müllerian ducts become abnormally developed – embryology

At the sixth week of gestation, the female reproductive organs develop out of the paired müllerian (paramesonephric) ducts – they fuse to create the uterus, cervix, and the upper two-thirds of the vagina. If this fusion fails, or the medial wall resorption/normal development doesn’t occur, a collection of congenital uterine abnormalities results.

There are currently seven classifications.

Unicornuate uterus

This is the result of an abnormal or failed development of one of the paired müllerian ducts, and is subsequently divided into four variations:

B – Isolated unicornuate (most common, 35 per cent of cases)
A2 – Unicornuate uterus – rudimentary horn present – non-cavitary (33 per cent of cases)
A1b – Unicornuate uterus – rudimentary horn present – cavitary non-communicating (22 per cent)
A1a – Unicornuate uterus – rudimentary horn present – cavitary communicating (10 per cent)

Urinary tract and kidney anomalies are also related, and have an increased incidence with a unicornuate uterus than any other müllerian duct anomaly.

References¹

1.
Khati NJ, Frazier AA, Brindle KA. The Unicornuate Uterus and Its Variants. Journal of Ultrasound in Medicine. Published online February 2012:319-331. doi:10.7863/jum.2012.31.2.319