The number of days between the first day of menstruation and the date of ovulation (the follicular phase) is variable, but the number of days between ovulation and the start of the next menses (the luteal phase) is generally rather constant at about 14 days. So if you have a menstrual cycle of 42 days, then you ovulate on Day 28 ! Add 14 days and your next menses will come. Therefore if you have a longish cycle then you ovulate late and your fetus will be less advance then it should be, meaning it will appear smaller or cannot be seen at all.
Of course, if for other reasons, the fetus has not grown, then it will also show up smaller. The way to get around making a correct diagnosis of which is which is to repeat a scan in about a week's time, so that those who are smaller because of a date factor will then be found to have grown. Question: I am 7 weeks pregnant and had a scan yesterday. My doctor said everything is fine and he could see the heart beat. He said the chance of a miscarriage is very small and he looks quite confident when he said that. Is the comment valid ? Answer: Nowadays most Obstetricians would believe that the cause of the majority of 1st trimester miscarriages is a defect in the embryo, and is basically a chance event. Imagine a sperm coming together with an egg to develop into a fetus.This involves many millions of cell divisions and changes so that the chance of something going wrong is very great. If it happens very early on in development ( say 4 to 5 weeks ), the growth of the embryo may come to a stop.The heart will cease to beat. The body in due course rejects the non-viable material, giving rise to the process of 'miscarriage'. Therefore if by about 7 or 8 weeks, everything appears intact with a good going heart beat, it is quite reasonable to say that the pregnancy will most likely carry on. (The statistics is actually on an average better that 95%, although it will be lower in women with recurrent miscarriages). Question: My wife is 9 weeks pregnant with twins, she has on and off bleeding and spotting for the past 3 weeks. She already had 3 ultrasound scans, all of which showed two fetal heartbeats. we are concerned ( because of the spotting and bleeding ) which leads me to ask two 2 questions: 1. What are the known causes of spotting and bleeding? 2. Given a "positive" ultrasound, how does that weigh against the fact that there has been occasional spotting and bleeding? Answer: It is always difficult to pinpoint the exact cause of bleeding in a first trimester pregnancy. In your wife's case, it could just be bleeding from the cervix or the edge of the placenta ( which is bigger and more close to the cervix because of the twin pregnancy ) and these situations generally bear little or no significance. Sometimes the bleeding can carry on up to the second trimester. If the heartbeat is present, the same still holds i.e. over 97% of the time the pregnancy will carry on unharmed. In the old days any vaginal bleeding in the early part of pregnancy is called ' threatened abortion '. With the advent of Ultrasound, we have to say this is a misnomer, as in the cases when the fetal heartbeat is seen, the pregnancy is not ' threatened '. Question: I had a scan yesterday. I am pregnant for about 30 weeks. My doctor said the fluid around the fetus is much decreased and told me to take more rest. He seems to look worried. Is this serious ? Answer: A decrease in the amount of fluid around the fetus (oligohydramnios) can be normal in most cases, and apparently can be improved with more rest, which in turn improves the circulation to the uterus.A significant reduction in the amount of liquor, however, is associated with retardation of growth in the fetus and possible congenital malformations. Your doctor looked worried because he might be unsure as to whether the fetus is suffering from an abnormality or not. In such a case, referral to a centre with expertise in scanning for fetal malformations may be indicated. But remember, most cases would be quite normal and bed rest with improve things. The amount of liquor around the fetus does not have any relationship with the size of the mother or how much water she is drinking everyday. Question: My doctor has diagnosed polyhydramnios. I am currently 33 weeks gestation. I was sent to a specialist for a more advanced sonogram and told that nothing is wrong other than the polyhydramnios. I had a tri-screen at 18 weeks and it was negative as well. I still can't help but worry that something is wrong. My concern is that a birth defect undetected by a sonogram may still be a possibility and that the doctor may be keeping something from me. He is reluctant to do an amniocentesis. It seems that they want to give me as little information as possible and I can't help but wonder why if everything is o.k. Answer: A detailed ultrasound examination at 33 weeks should be able to diagnosis most, if not all the recognizable causes of polyhydramnios. A significant proportion of pregnancies with polyhydramnios does not have any demonstrable birth defects in the fetus. An amniocentesis may indeed be helpful for planning necessary treatment but your doctor probably felt that the chance of finding something wrong with the amnio is too small to warrant doing it. That is actually good news. I don't think your doctor is trying to keep things away from you. Question: My doctor said that my baby's head is a little 'smaller than dates' whereas the limb bone and the abdomen were quite on par with dates. Does that reflect that I have a baby with an abnormal head ? Answer: If this is your first scan, then it may be a problem with dates. If your dates have been quite well validated from a previous scan, then it appears your baby could have a slightly smaller head. But so what ? All of us has a different size head, isn't it ? And mind you, your doctor measures the side-to-side 'diameter' of the fetal head and if your fetus has a relatively 'flatter' head it will appear 'smaller' on measurement. This may simply reflect the head's configuration rather than anything that you should be alarmed about. It will need a size lag of up to 3-4 weeks before one would start to consider malformations such as microcephaly ( small head syndrome ). Question: I had a scan at 8 weeks and my doctor said the fetus is only 7 weeks, and it was because I had irregular menstrual cycles. I had another scan at 34 weeks and my doctor now said the fetus size was only 31 weeks. Should I stick to the earlier scan or should I use the later scan to fix my Due date ? If my fetus is smaller, would it be wise to leave it in the womb for as long as possible so that it can grow bigger and get more mature ? Answer: You should always use the result of a scan that is done earlier on in pregnancy for 'dating' purposes as it will be more accurate. In the later part of pregnancy the measurements will be affected by growth variations and will no longer reflect the fetal 'age' correctly. In your case, the findings apparently indicated that you have a smaller than average baby. It is incorrect logic to think that babies who are not growing well should be left inside the womb for a longer period of time. In fact the reverse should be true. The baby may be better off outside than in and for this reason we sometimes have to deliver these babies well before the actual due date. Question: I had a scan at 34 weeks. My doctor said the estimated weight of the fetus is 2.0 Kg. Is this too small? How much should an average baby weigh at 34 weeks ? Answer: The weight for an average size fetus at 34 weeks is about 2.2 Kg. 2.0 Kg will be on the 25th percentile line. We would say a baby is small-for-dates when it's weight is below the 10th percentile line, and in the case of 34 weeks this will be 1.8 Kg. Please take a look at the Intrauterine weight chart. Your baby is on the small side, but not too small. You must also know that estimating the weight of the fetus with ultrasound measurements sometimes can incur errors of over 10 percent. Your doctor will usually make an assessment together with other ultrasound findings. Question: I will have a scan tomorrow. What is the chance that I would be able to see the sex of my baby on the screen? I really do not want to know this before the baby is born. Answer: The chance that you will recognize the genital organs of the baby without any prompting is very small. Interpretating an ultrasound image requires a lot of training and skill and is not like looking at a photograph of a person taken in front of him. Patients are often unable to 'see' the parts of the fetus the doctor is actually carefully studying during a scanning session. Question: A friend of mine was seen at the ER because of pain. She was pregnant for about 7 weeks. They did a scan and found no sac in the uterus and asked her to go home. Two days later she was admitted again to another hospital with massive bleeding from an ectopic pregnancy. Why was this initially missed on the scan ? Answer: Ectopic pregnancyis notorious for not being diagnosed early, as the physician has always to exclude basically 3 other conditions in early pregnancy which give rise to pain.1. She can have pain for no apparent pathology in early pregnancy, probably as a result of of uterine and venous engorgement.2. Missed or inevitable abortion.3. Ruptured ovarian cyst or pain arising from other abdominal organs.Ultrasound, unfortunately, will not be able to make a 'definitive' diagnosis of ectopic pregnancy in most of the cases as it is often not possible to visualize the actual gestational sac in the fallopian tubes. The fact that there is no gestational sac seen in the uterine cavity may just mean that the pregnancy has not been growing normally or that some sort of an abortion might have occured or that the pregnancy, due to to an irregular menstrual cycle in the woman, is much less advance than is thought.The doctor often needs to take into account of the menstrual history, the time she had a positive pregnancy test, the intensity of the pain, physical signs, a blood count and findings on ultrasound scan. Question: I would appreciate any information on molar pregnancy that you can provide. Last year I had emergancy surgery done because of this condition. I was told very little information about it at the time. I was wondering specifically: what exactly does it mean to have a molar pregnancy, what causes this, what are the chances of having one, and is normal conception/pregnancy difficult for someone who has had one. Again, any information on previous studies of this condition is appreciated. Answer: I am afraid I won't be able to give you detailed descriptions about a specific disease. May I suggest that you use the search engine "Google" or "Alta Vista" to find the answers you need. http://www.google.com/http://www.altavista.com/You can also use the DejaNews engine to search the Newsgroups.http://www.DejaNews.com/I am sure you will find plenty of information that you need. Question: My wife has already had 5 scans in her present pregnancy because our doctor thinks the baby is not growing very well. I am worried if this may be harmful to the baby. Can you tell me where I can find some information concerning the safety of ultrasound in pregnancy? Also, why does she need to be scanned so many times ? Answer: Please read the section on Safety references. There is presently no evidence of a cumulative effect of ultrasound in the fetus. Your doctor probably wanted to monitor the growth of the fetus by taking body measurements at set intervals. If the growth lag is getting serious, he would have to perform some other tests to monitor the wellbeing of the fetus and perhaps act promptly to deliver the baby at an earlier date. Question: I went for my ultrasound yesterday (20 weeks and 2 days). I also had one at 17 weeks and the technician said she did not see any boy parts, and advised me to come back for a repeat scan. Well I went yesterday, and she said there were definitely no boy parts down there, and she started looking for the labia. She could'nt see the labia after searching for about 10 minutes and told me that since by this time they can almost always see the penis or scrotum, she felt this baby is a girl, although she didn't seem to look that reassuring. We were able to tell our sons were boys at 18 and 20 weeks so I am wondering why this time it's so difficult. Is it unusual not to see the labia at 20 weeks, and does that mean it can still be a boy ? Answer: I can see that you are quite anxious to know the sex of your baby. In order to be certain the sonographer should reassure himself that he actually sees the penis and scrotum in the case of a boy and the labia in the case of a girl. The absence of the penis must not be taken as sufficient evidence of the fetus being a girl. Your sonographer was careful not to make a mistake which could be extremely embarrassing. Most of the time one should be able to tell the sex of the baby by about 20 weeks and very often even at sixteen. On the other hand, as the correct visualization of any fetal part depends of a host of factors such as fetal position, amount of liquor and thickness of the abdominal wall, I have had occasions when I cannot be certain about the sex even at 28 weeks. I have been repeated asked many many times about just how accurate is the diagnosis of fetal gender by ultrasound? Well, I have to say that it should be very accurate (somewhere between 95 and a hundred percent), particularly after about 20 weeks, or even sixteen. However I must say again that one must remember the sonologist may not always get a good view of the perineum (private parts) of the fetus for a variety of reasons and therefore may not furnish you with an "accurate" answer. One really needs to put this question to the person who performs the scan. He or she is the only person to be in the position to tell you just how accurate "that" particular diagnosis is. Question: I have heard that the heart rate of the fetus is slower when the fetus is male ( less than 140 per minute ), is this true and when is the best time to count the heart beat to tell the difference ? Answer: There is no scientific basis for a difference in heart rate between fetuses of the two sexes. It is another of maternity's many myths. Please read a very good article on this subject by Terry DuBose. Question: I am 18 weeks pregnant. I went for a routine scan yesterday and I was told my baby has a small cyst in the brain. My doctor said she would like to scan me again in 2 weeks time to see if the cyst grows any bigger and if there are other things wrong with my baby. She mentioned something about chromosomes. Is my baby going to be very sick or mentally retarded ? Answer: I think your doctor probably saw a "choroid plexus cyst" in the fetal head. This occurs in about 0.5 to 1 percent of fetuses and the great majority of them will disappear eventually. They have, however been found to be associated with chromosomal abnormalities notably Trisomy 18 and trisomy 21 (some 5 to 30 percent of these fetuses have the cysts). It is probably worse if there are more than one cyst and they are bigger than 10mm. Single cyst is almost always benign. It is important to diligently check for other features of chromosomal trisomies in the subsequent scan. An amniocentesis may be ordered if findings are in doubt. Try to read this article in the Birth.com.au Question: Can you tell me just how accurate is ultrasound ? I heard that abnormalities can sometimes be missed by a scan. Answer: There is no definite estimate of exactly how accurate ultrasound is at detecting disabilities, and there are both false negatives and false positives. As far as detecting fetal abnormalities goes, several points have to be bornt in mind :a) Not every problem can be diagnosed with ultrasound -- conditions which do not manifest as a structural or gross functional abnormality (such as a very abnormal heart beat or mental retardation) may be missed.b) Not every problem which can be detected will be diagnosed. For example, in many ultrasound examinations the baby's fingers and toes are not counted, even though it is possible to do so should it be necessary.c) The ability to detect abnormality in the fetus at an ultrasound exam depends on a number of factors, such as the size and position of the fetus, the amount of amniotic fluid around the fetus, the body habitus of the mother (whether she is fat or slim), the type of equipment used, and, most importantly, the skill and experience of the operator.d) Some problems (such as anencephaly) are more readily diagnosed than others (such as cleft palate).The accuracy of ultrasound for dating a pregnancy depends on at what point during the pregnancy the ultrasound is taken. Pregnancy dating is most accurate during the first eighteen weeks of pregnancy. Measurement of the sac at five to seven weeks is not accurate. Measuring the crown-rump length gives an accuracy of plus or minus three days at seven weeks; this test can be used from the seventh to the fourteenth week. Between fourteen and twenty-six weeks, measurements of the biparietal diameter, the femur length and abdominal circumference are generally used. The accuracy is plus or minus seven to ten days. The accuracy further declines with advancing gestation age. Question: What is meant by a Level II ultrasound examination? Answer: A level II ultrasound examination refers to a 'targeted' examination. This is usually performed at a perinatal center where more expertise in ultrasound scanning is available. Situations when a level II scan is ordered include:suspected fetal anomaly during a level I examination, severe IUGR, elevated maternal-serum AFP, Oligohydramnios, polyhydramnios, two-vessel umbilical cord detected at the level I examination, fetal cardiac arrhythmia, and exposure to drugs or chemicals in the first trimester....etc. Detailed scanning for any congenital anomalies and growth abnormalities is done on top of the basic documentations obtained at the level I examination, which refers to:in the first trimester, a. documentation of the location of the gestational sac. b. documentation of the crown-rump length. c. documentation of the presence or absence of fetal life. d. evaluation of the uterus (including cervix) and adnexa. in the second and third trimester, a. documentation of fetal life, number, and presentation.b. documentation of an estimate of amniotic fluid volume. c. documentation of placental location. d. documentation of gestational age. Assessment of the BPD, FL, AC and othe fetal parameters.e. documentation of basic fetal anatomy (including a basic 4 chamber view of the heart, spine, stomach, kidneys, bladder, umbilical cord insertion ... etc ). One should not not dwell too much on the definitions or guildlines for a level II ultrasound scan. In a level II scan the sonologist should try as hard as he can to look for and assess any abnormality that is present in the fetus. It's meaningless to be thinking about level III or even level IV scans. Question: My wife never had a scan for her present pregnancy. I have heard that in many hospitals an ultrasound scan at about 20 weeks is routine. Why is it not done in my wife's case ? Answer: The issue of 'Routine scans' in a 'low risk' patient is still a matter of some debate at the moment. I personally is for the implementation of the policy of a routine scan for every pregnancy at 18-20 weeks. Few people will doubt it's usefulness in improving gestational age dating, in the early recognition of fetal anomalies, in the identification of intrauterine growth retardation and of multiple gestations. There is apparently a distinct difference in the attitude towards routine ultrasound screening between the Europeans and the Americans. Routine screening scans were introduced in Germany in 1980, in Norway in 1986 and in Icelend in 1987. The scans basically try to date the pregnancy, exclude twins and detect any fetal malformations that may be present. In the U.S., routine scans in pregnancy has however been looked upon with much controversy and their cost-effectiveness and validity in improving 'quantifiable' perinatal outcome has not been firmly established. Nevertheless, those who argue for a routine scan would claim that parents have a natural desire to know if any fetal congenital anomaly is present or if there is any health compromise in the fetus. Being able to reassure the parents is a natural part of prenatal care. Two important large scale studies emerged to address the issue: the RADIUS study (Routine Antenatal Diagnostic Imaging with Ultrasound) with a cohort of 15,000 low-risk pregnancies in the United States in 1993 and the Eurofetus Study in Europe in 1997 in which 200,000 low-risk pregnant women in 60 hospitals had obstetric ultrasound examinations performed in centers proficient in prenatal diagnosis. A 61% overall detection rate of structural anomalies in the Eurofetus study contrasted sharply with the 35% overall detection rate in the RADIUS study. In order to address the conflicting data and conflicting opinions on this topic, a conference was held at The Rockefeller University in New York City, in June 1997, sponsored by the New York Academy of Sciences. Over 150 scientists and clinicians participated in the meeting, with highly informative presentations and discussions. Apparently the following conclusion was made: " .... In summary .... we have tried to put together comprehensive state-of-the-art information on the routine obstetric ultrasound controversy. Our conclusion .... is that routine obstetric ultrasound is warranted for all pregnancies, but only if it is performed in a quality manner. Although there is still scientific and economic controversy about our conclusion, we would argue that, at a minimum, there is an ethical obligation to present the option of an 18-22-week routine obstetric ultrasound examination in clinical centers in which quality ultrasound is available. We hope that our efforts will move public policy in this direction and encourage further discourse on this most important topic in contemporary obstetrics." In a setting with routine scanning, the cost of healthcare could be greatly increased. Such cost-effectiveness consideration is likely to be of concern at the hospital where your wife is attending. For an individual private patient I have absolutely little hesitation of ordering a scan at 18-20 weeks on a routine basis.
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