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Pregnancy Bliss | Reproductive Health Hub

Discrepancy between my own and scan dates

Question:  According to my LMP I am just over 8 weeks pregnant. I was tracking ovulation so can say with some degree of accuracy that is correct. Also did a test which showed me to be 4-5 weeks pregnant 4 weeks ago. However I went for an early scan last week (when I would've been just over 7 weeks) and the CRL was 0.47cm which she dated at 5-6 weeks. It was an abdominal scan. Neither the sonographer nor my midwife seem concerned and there was a heartbeat etc, and I've had no bleeding, but I've read online that it's not a good sign. Is it possible the scan was this far out? L.P. (USA)


Answer: This is a slightly puzzling case. If your pregnancy test was definitely positive 4 weeks ago, by implication, it means the minimum gestation you can be is 8 weeks. This is on the basis of the fact that a pregnancy test is expected to become positive at the earliest when you are 4 weeks gestation (2 weeks after conception). On that basis alone, the scan findings would be a cause for concern. However, there is always that small possibility that the pregnancy test was falsely positive when you first did it. Admittedly, that assumption appears a little far-fetched on the basis of what we know.


It is a little frustrating that your scan results were given in centimetres rather than the standard millimetres. This is not being pedantic. It can create confusion for some expectant mothers when seeking information elsewhere (especially online). Working on the premise that the measurements were in fact correct, the 0.47cm would be 4.7mm. That is why the gestation was put at a seemingly bizarre ‘5-6’ weeks. This would be because most Crown Rump Length (CRL) charts start at 6 weeks. A 6 weeks fetus CRL is 5mm i.e. just above the 4.7mm that your baby measured. The reported results had me wondering whether the sonographer actually measured 4.7cm (47mm). That would be equivalent to 11 weeks and 3 days. If only she had stuck to millimetres… I am sorry that I may not have provided the clarity that you seek and deserve. I would suggest that you try to get another scan, ideally about 2 weeks from the last one to get that clarity. My best wishes.







Poor trophoblastic reaction on scan

Question:  I got my first US done today. States that “There is a single gestational sac of normal shape, size and location within the uterine cavity.The trophoblastic reaction is poor. The yolk sac and foetal pole are well visualized. Normal cardiac activity is seen in foetal pole. The crown lump length measures 4.7 cms corresponds to 6 weeks 1 day of gestation.

The gestational sac measures 1.90 cms,

Internal os is closed.

Clear cyst in right ovary of 29 mms.

Q - what does the above mean? is it good or bad?

What is trophoblastic reaction? what does it mean if it is poor....

Will it be possible for me to carry the entire term is this is poor? What precautions should i take. N.S. (India)


Answer: There are a number of issues in this report but the most glaring one is the crown rump length (CRL). I cannot quite work out why the reported CRL of 4.7cm (47mm) was said to be equivalent to 6 weeks and 1 day.  One or the other must be wrong. If the CRL was indeed 47mm, that will be equivalent to 11 weeks and 3 days. If the gestation is 6 weeks and 1 day, the CRL would be a mere 5mm i.e. almost a tenth of the reported length.

For that discrepancy, you will need to get a clarification. As for the reported ‘poor trophoblastic reaction’, that is usually a feature that would cause concern. When it is seen in threatened miscarriage (bleeding in early pregnancy), it could indicate that the chances of miscarriage taking place are substantial. Trophoblastic reaction is seen at the interface between the wall of the uterus and where the implantation takes place. This is where the placenta will eventually form.


The rest of the scan report  reads normal and it is difficult to work out where the apparent ‘poor trophoblastic reaction’ fits in. Unfortunately you did not provide me with the details of your pregnancy in terms of gestation by your own dates. In any case, you should have the discrepancy between the recorded CRL and the given gestation sorted out.




Risky infections in early pregnancy

Question:  Hi, I am manager of a busy day nursery. I have a few staff who are in their first 12 weeks of pregnancy. Please could you send me details of any illnesses that they should be kept a way from? L.A. (UK)


Answer: Young children are susceptible to a whole variety of viral infections. This is for the simple reason that they lack active immunity. Once the passive antibodies they get from their mothers in the womb run out, they can only get immunity by acquiring the specific infections or being vaccinated for the infections deemed dangerous (such as measles). Infections that will be a concern especially in early pregnancy are chickenpox and Rubella (German measles). The challenge you may have is the fact that Rubella has non-specific symptoms, usually described as ‘flu-like’. As such, you may not know when a toddler has this infection. On the other hand, it is the case that most adults in the UK will be immune to rubella as a result of being vaccinated earlier in childhood. Most children too receive the MMR vaccine so they are likely to be immune. There are other less common viral infections such as parvovirus but the truth of the matter is, these are almost impossible to recognise and therefore impossible to guard against. I need to stress that these are quite uncommon. Infections have been discussed in a dedicated section here:














In early pregnancy, fetal size is done by measuring the length from the top of the head (crown) to the bottom (rump) giving the Crown Rump Length (CRL). This is the only reliable way of estimating gestation before 13 weeks of pregnancy. It is very accurate. Measurements should be given in millimetres (mm).