Ultrasound, Date My Pregnancy, Smoking Effect

ConcernedDad Asked :

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My wife is 14 weeks pregnant from our estimation, and she went for her first pregnancy ultrasound last week. I know it is a bit late but due to personal beliefs, we did it at this time. The gynecologist estimated that she is in her 16th week of pregnancy after doing the ultrasound. We are almost dead sure that she was 14 weeks pregnant because of her last period and the first positive result we got on a home pregnancy test.

When we saw our doctor in the first 4 weeks, he had also requested some blood tests and had confirmed the stage of pregnancy which matched our estimate. I am now confused. What is going on? Are these pregnancy dates accurate? My wife is a smoker and she has assured me that she quit smoking. Could smoking have affected the pregnancy date assessment?

This is very important to me personally because it has a major impact on me as to when the baby was conceived or if the baby is growing properly. I should mention that my wife did miscarry once previously but we had not planned for a baby at the time and she was not very healthy at that stage.


This question was posted under the Ovulation Schedule article.

Any response by the Health Hype team does not constitute a medical consultation and the advice should be viewed purely as a guide. Always consult with your doctor before making any changes to your current treatment program. The information provided in this article is not an authoritative resource on the subject matter and solely intends to guide the reader based on the questions asked and information provided.


Dr. Chris Answered :

Estimating the stage of pregnancy can be done by a number of methods and from what you say, there are 3 methods that have been used thus far. Firstly, estimating the pregnancy date (gestational age or GA) by the last menstrual period (LMP) is not extremely accurate and a lot depends on regular menstrual cycles. It is not a method that should be used in isolation.

Secondly, the blood tests that your doctor requested is probably the quantitative and qualitative beta-HCG. Qualitative will confirm pregnancy. Quantitative will give a reading of the level of beta-HCG present in the blood with anĀ  estimated range of the pregnancy date (in weeks). The quantitative test is useful in assessing a miscarriage as the beta-HCG levels rise exponentially in a healthy pregnancy. However, in a miscarriage, there may still be a rise in beta-HCG levels but it is not as high as would be expected.

Your doctor may have conducted this test considering your wife’s previous miscarriage. He may not have done it for the purpose of estimating the pregnancy date. You do not mention an ultrasound at this stage so your doctor probably made the assessment based on your wife’s last menstrual period and quantitative beta-HCG. This may be inaccurate and an ultrasound should have been done within the first trimester.

Thirdly, the ultrasound that was conducted last week may have used one or more of the following to assess the gestational age – biparietal diameter (BPD) and head circumference (HC). Both of these use head measurements to make an assessment. Less frequently the femur length (FL) may be used but this is not accurate given a number of variables.

An ultrasound is fairly accurate for measuring the gestational age but you must remember that this is just an estimate. This pregnancy date that your doctor gave you can vary to some degree. Since this is the first ultrasound, you should not take this estimate as the final result. Rather wait for follow up ultrasounds and you may still experience some variations in gestational age.

In terms of smoking, it can affect the baby’s birth weight (leading to low birth weight) and there is a possibility that it could have affected the fetal growth. This MAY have affected the pregnancy date estimate. This is no way to prove that your wife is currently smoking and even if she has quit, the effects of long term cigarette smoking can persist.

Lastly, it is important to bear in mind that home pregnancy tests may have a varying degree of accuracy. Some will detect beta-HCG in the urine within the first week. Others will only detect it a bit later. Speak to your family doctor or the gynecologist about your concerns. Both will be glad to help you and provide more information. Do not make assumptions based on the information you have received thus far.

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