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, since these anomalies usually come to light after investigations for fertility, so the general population isn’t taken into full consideration.
- 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
- 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)
- 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
- Primary amenorrhoea (periods don’t commence)
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.
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.
The Unicornuate Uterus and its Variants, Clinical presentation, imaging findings, and associated complications, Nadia J. Khati, Aletta A. Frazier, and Kathleen A. Brindle