In a significant number of pregnancies, there is a controversy as to the exact gestational age of the pregnancy. This may be as a result of the use of hormonal agents that disrupt the normal cycle before pregnancy. It may also be due to prior irregular menses, abnormal vaginal bleeding, the woman’s forgetfulness, absent menses from other causes before she got pregnant, pregnancy while still breastfeeding, etc. Sometimes too unfortunately, the lady is further confused by the different scans that she has done. At our center, we follow the established international standards for gestational age estimation.
    The commonest method traditionally used for gestational age is calculation based on the first day of the last menstrual period. Reliability on this date depends on prior regular menses. This date becomes acceptable for calculation if it does not differ significantly from the dates based on measurements done at an early scan not beyond 5 months. If there is a significant difference from that of the scan, and if the measurements of the different structures correspond to each other, then the dating from the scan is used. The gestational age based on the earliest of these measurements, if done by a reliable sonographer, is maintained throughout the pregnancy. The expected date of delivery (EDD) does not change if a later scan is done that gives an apparently different gestational age.


    The detection of an anomaly in the fetus some months before delivery can be quite distressing to the parents. This is worsened by the fact that it is difficult to exactly predict how these anomalies will affect the fetus. Based on this, many parents may opt not to know the findings. It is important to inform the sonographer of your wishes before the start of the ultrasound examination. Fortunately, the chance of a fetal anomaly in the general population is quite low. It is also important to know that the fact that no anomaly was found on ultrasound is not a 100% guarantee of complete health of the baby. Nevertheless, such normal scans are quite reassuring.


    Maternal age and obstetric ultrasound
    It has often been reported that women of advanced maternal age (greater than 35or 37 years on the average) have an increased risk of chromosomal and other inborn abnormalities of the fetus. It is based on this that screening ultrasound scans and the accompanying invasive procedures are often recommended for pregnancies in these circumstances.
    In ideal circumstances, it is advocated that these mothers have a first ultrasound as early as possible in the pregnancy (usually by the second missed period or before) to diagnose that there is a pregnancy, that it is alive and then to accurately date the pregnancy. Based on this, a screening scan is done at between 11 and 13 weeks. This could help rule out major anomalies and to assess the risk of chromosomal anomalies. If the pregnancy screens high, an invasive procedure for diagnosis (CVS) is done. If necessary, a 22 week anomaly scan may be repeated. Thereafter, ultrasound examination could be as indicated.

  • Previous adverse pregnancy outcome
    This is repeated here for the purpose of emphasis. Pre-pregnancy counseling is advised. Depending on the findings, management is offered. When pregnant, such pregnancies are best managed by a specialist in a specialist center. Early booking is encouraged with an early scan at about 6 to 8 weeks. Thereafter, a screening scan at 11 to 13 weeks is important which could include Doppler screening for preeclampsia and other placental diseases. Thereafter, an 18 – 22 week scan may be done. Follow up with Doppler scan is necessary from about the 28th week to assess fetal health and well being and may assist in planning delivery.


    Multiple pregnancy
    Many women are alarmed when told they are expecting twins, triplets or other forms of multiple pregnancy. However, there is no need to be unduely alarmed. Multiple pregnancies present challenges that can be managed with extra care and increased surveillance. It is virtually impossible to know from the beginning how many babies there are. Suspicious signs of multiple pregnancy include excessive symptoms of pregnancy especially vomiting. Much later in pregnancy, it could be noticed that the womb is larger than expected for the age by dates. However, ultrasound scan can be helpful in making an accurate diagnosis of multiple gestation.
    Ultrasound diagnosis of multiple pregnancy can be made from about 6 weeks gestation. At this time too, one may have an idea of the type of placentation. This last information is important in the management of the multiple gestation as it determines the risk. Those with shared placentae (monochorionic in twins)require closer monitoring than those with different placentae (dichorionic in twins). For those with suspected multiple gestation therefore, an 11-13 week scan is absolutely essential to plan the management. Thereafter, an 18 to 22 week scan is done following which based on the findings, regular scans can be arranged.


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