‘Vita’ in Latin means alive and the term viability may have been derived from this notion and the opposite is considered as non-viable . Therefore, a non-viable pregnancy indicates a fetal demise or most commonly known as a miscarriage in clinical terms. In return it is also known as a spontaneous loss of a fetus before it can survive independently (after 24wks.). Miscarriage can be further sub divided into many forms depending on the symptoms presented and from the ultrasound appearances. Most commonly identified symptoms of a miscarriage are seen as heavy vaginal bleeding, discharge and severe cramps and abdominal pain. The types of miscarriages are identified as:
- Anembryonic Miscarriage – No embryo formed from the fertilised egg, only a gestational sac develops. Women may be asymptomatic or some vaginal bleeding.
- Missed Miscarriage – Is when the fetus has implanted but however fails to develop as viable and no symptoms of miscarriage are seen.
- Incomplete Miscarriage – Some of the tissue from the pregnancy remains in the uterus with accompanying vaginal bleeding.
- Complete Miscarriage – is defined as all of the pregnancy tissues have been expelled out of the uterus in a woman who’s already had a previous US.
- Inevitable Miscarriage – Unexplained vaginal bleeding and presence of open internal Os. Gestation sac or the retained products seen in the lower part of the uterus.
- Molar pregnancy – can be complete or partial in nature. A non-viable blastocyst implants in the uterus due to incorrect genetic material (sperm to sperm fertilisation) and forms a large cystic mass.
- Ectopic pregnancy – Implantation of a fertilised egg outside of the uterine cavity, usually embedded in the tubal portion.
- Failed early pregnancy – Nonviable fetus in a correctly positioned gestation sac in the uterus.
To determine further the exact type of miscarriage usually a Transvaginal (TV) US is performed. TV is better than trans abdominal (TA) approach as TV can get closer to the structures with a higher frequency probe providing better resolution of the pathologies. The smaller structures in early pregnancies are seen optimally with a TV probe. The advantages of using US as an imaging modality in these cases are that it is an inexpensive and a fairly quick examination under a trained operator. The results can be given after the scan with cross reference to blood and hormonal test results. US also has no bio effects from ionising radiation that can harm the fetus. Some limitations of using TV approach is the intrusive nature of the examination, and some woman therefore may be less inclined to see the benefits of it and may decline. TA can be used in early pregnancy if bowel gas and large fibroids are obscuring the uterus in TV method and to get a good overview of the surrounding peritoneum.
In regards, to the case presented above US findings of a viable intrauterine pregnancy at 12 wks. should be scrutinised against abnormal findings.
Normal viable pregnancy at 12 wks. gestation should present with an intra-uterine sac with a fetal pole and fetal heart pulsations seen clearly with limb buds, cranial vault mineralisation and the fetal bladder, stomach. Normal appearance of a gestational sac is seen as uniformly oval shaped structure surrounding the double decidua sign implanted eccentrically in the fundus of the endometrium. Yolk sac can be seen as a spherical shaped structure with a hyperechoic ring after the 5th wk. of gestation. By the 6th week fetal pole should be visualised and measures up to 9mm and fetal heart pulsation should be visualised. By 7th week limb buds start to form, and mid gut herniation should be visualised as a normal variant. At 12 weeks, fetal pole should measure between 45-84mm in size with cardiac activity. Ovaries difficult to see at this time, however a corpus lutem cyst should be seen with internal low level echoes in a thick walled and a crenulated inner margin with peripheral vascularity seen as ring of fire
If a pregnancy (fetal pole with cardiac activity) is seen in the uterus with the normal structures and CRL doesn’t corresponds to the dates, it is important to ask the patient of the last menstrual period and when the first positive pregnancy test was carried out. If these are discordance with each other, NICE guidelines are followed in uncertain cases. Findings can be closer to the decision boundaries of a miscarriage of the CRL is < 7mm with no fetal heart pulsations and mean sac diameter (MSD) < 25mm with no fetal pole seen. If in TV approach MSD is > 25mm but no fetal pole seen second opinion and/or rescan should be undertaken. Similarly, CRL >7mm with no cardiac activity should be verified with a second opinion and/or rescan in 1 week. Absence of an embryo after 6 weeks of gestation is another sign to alert the practitioner of a missed miscarriage. Another feature to suggest discordant viability is an enlarged yolk sac with empty amnion sign. If sub chorionic haematoma or an irregular sac is presented centrally in the uterine cavity, a pseudo sac should be considered and pregnancy of unknown location (PUL) need to be further investigated through bhCG levels over a 48hr window.
This leads to the question of how US findings can be further scrutinised to gain an understanding of the type of miscarriage is observed in the given scenario. With the information given in the context of symptoms presented this should be considered as a failed early pregnancy or if a pseudo sac is presented an ectopic pregnancy should be investigated in the PUL pathway. If the scan further showed a large solid mass with cystic spaces (heterogenous appearance in the uterus) a molar pregnancy should be suspected. If a definite fetal pole is also not seen, then anembryonic miscarriage can be diagnosed. Hence, this indicates the clear need for more information from the patient as well as from the GP who referred the patient with this type of symptoms in early gestation.
TV approach plays an important role in the diagnosis of different types of miscarriages observed clinically and whilst it may be useful to gain an understanding of the diagnosis it is also important to treat these women with utmost sensitivity in delivering bad news and further providing access to advice/support through an early pregnancy unit.