Recurrent miscarriages

 

The WHO defined a miscarriage as pregnancy loss of a fetus 500 g or less in weight. However  clinically diagnosis relates to pregnancy loss between 5 and 20 weeks.

Sporadic loss of pregnancy is estimated to occur in 15-25% of clinically recognised pregnancies but could exceed 50% of all conceptions. It is estimated that approximately 5% of women have 2 miscarriages and <1% have 3 consecutive miscarriages which is described as recurrent.

Depending on the gestational age a miscarriage is described as early or late if it occurred before or after 12 weeks respectively.  Early miscarriages could be further sub classified into:

• Biochemical with a positive βhCG but no gestation sac on ultrasound scan examination.
• Anembryonic when there is no yolk sac with a 20 mm gestation sac and no fetal pole with a gestation sac of 25 mm or more.
• Embryonic when there is no fetal heart activity in a 6 mm CRL fetal pole or loss of a previously observed such activity.

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  Causes of recurrent miscarriages

 

Though recurrent miscarriage is traditionally defined as 3 consecutive losses no difference was seen in the risk of further miscarriages after 3 or 2 losses. This risk is 30-45% or 30% after 3 or 2 miscarriages respectively. Accordingly patients could well be investigated after 2 losses. In all cases the rate of pregnancy loss increases with age.

 

However in a good percentage of cases [50%]  pregnancy loss is unexplained and could not be attributed to any specific cause. Almost all suspected causes could be included within few major groups. 

1. Problems with the pregnancy itself
2. Problems with the pregnancy environment

For more information regarding problems related to the first group please see the relevant section in my other website www.gynaecology.spotmysite.com

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Problems with the pregnancy environment

This includes a long list of factors and transvaginl scan examination could have a major role in the diagnosis.

Anatomical factors 

 

Historically cervical incompetence was the most suspected anatomical cause of repeated second trimester miscarriages though the evidence has not always been overwhelming. It is defined as inability of the cervix to support a pregnancy to term due to functional or structural defects. It is prevalent in 0.2 % of the general obstetric population but in 8% of women with history of previous midtrimester miscarriages. Animal studies documented defective tensile strength of the cervix due to rearrangement or disorganisation of the collagen fibres.

Unfortunately there is no objective diagnostic test to be done in-between pregnancies and clinical suspicion is most important as hysterosalpingography and painless passage of size 8 dilator into the cervical canal are not reliable.   

However during pregnancy 3 ultrasound scan criteria are used to help with the diagnosis. Transvaginal scan examination gives good quality images and hence helps more with the diagnosis. The 3 criteria are: 

• A short cervix is a good parameter to use. Shortening of te cervix during repeated examinations could follow increased uterine muscle activity or inherent cervical disease. 
• Dilated internal cervical os leading to the characteristic ultrasound funnelling effect. Together with the short cervix they could facilitate ascending bacterial infection which could weaken the exposed membranes.
• Prolapsed membranes  

Uterine anomalies both major and minor are prevalent in 7-8% of fertile women and in more than 25% of women with recurrent miscarriages. However major anomalies prevalence was estimated to be 3% in fertile and infertile women but 5-10% in patients with recurrent miscarriages. Uterine anomalies are related to mullerian ducts  complete or partial failure of fusion or failed canalisation.

A summary of the reproductive performance of women with uterine anomalies is as follows:

• Arcuate uterus with a concave upper cavity of < 1 cm intrauterine indentation has no impact though contradictory reports have been published suggesting more second trimester and pre term delivery with this anomaly.
• A septate uterus has 25.5 % risk of miscarriage but its impact on infertility is less known. With continued pregnancy there is increased incidence of of malpresentation and caesarean section rates. After incision of the septum there is 2-3 fold improvement in pregnancy outcome but it does not improve pregnancy rates in infertile patients.
• A bicornuate uterus is associated with slightly increased risk of second trimester miscarriages and preterm deliveries problably due to an associated cervical incompetence. It is not recognised as a cause of first trimester pregnancy loss and does not cause infertility. Unlike the septate version surgical treatment is not usually indicated and might be resorted to as a final option. Follow up of the patient with serial scans for early detection of cervical incompetence and insertion of a cerclage is the first line of management. Should surgery be indicated, it should be transabdominal or laparoscopic but not hysteroscopic.
• Didelphic uterus is associated with 20% miscarriage rate and 24% preterm delivery rates.
• A unicornuate uterus has significant effect on reproduction due to abnormal uterine vasculature and decreased muscle mass. The ectopic rate is increased to 4.3%,   miscarriage rate 34.4%, preterm labour 43.3% and live birth 54.2%. Moreover there is a high caesarean section rate with this abnormality due to malpresentation and abnormal uterine contractions. It has a banana shape cavity on transvaginal ultrasound scan examination.

Coronal view of arcuate uterus	Coronal view of a  septate uterus	Coronal view of a sub septate uterus	Unicornuate uterus after saline infusion	2D view of double uterus

Fibroids

 

The presence of submucous fibroids is widely accepted as a cause of recurrent pregnancy loss. As well recent research showed that relatively large intramural fibroids [> 4 cm in diameter] could compromise reproductive performance.  Lower implantation rate following IVF has been described in such cases even without involvment of the uterine cavity. The best way to assess how much the cavity is affected by a fibroid is through saline infusion sonohysterography which would show how much of the fibroid extends into the uterine muscle as well. This is an important information which could not be asecertained with hysteroscopy yet it is important for deciding the best surgical approach to remove such fibroids.

  

Coronal view of a uterus with a submucous fibroid	A submucous fibroid as seen hysteroscopically

 

Intrauterine adhesions

 

These are scar tissues which form inside the uterus as a result of infection or previous surgery. They could complicate any surgery involving the uterine cavity especially evacuation of retained products of conception. They could reduce or stop menstrual blood loss, cause infertility or repeated miscarriages. Usually patients give history of such procedures during consultation.  As well saline infusion sonohysterography is the best method for diagnosing intrauterine adhesions. In severe cases and with apical synechiae obstructing the isthmic part the uterine cavity would fail to distend with the fluid.  

Intrauterine adhesions shown as filling defects  disturbing the cavity after SIS	Intauterine adhesions with a fibroid seen  hysteroscopically

Large endometrial polyps

These are tumours of the basal endometrium with fibrous stroma and central blood vessels. Large polyps could compromise early pregnancy and would need to be removed.

   

Endometrial polyp in a sagittal view of the uterus	Large endometrial polyps