Episode 20 21-week Antenatal Visit

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Hello. This podcast is called the 21-Week Visit. Mum, baby, morphology scan, vaccines, record-keeping and continuing health education.

My name is Dr Elizabeth McCarthy, known as Liz, and I'm an obstetrician, subspecialist in maternal fetal medicine and heavily involved in teaching women's and newborn health at the University of Melbourne. This podcast is about what happens in antenatal clinic for women who have had their mid-trimester scan and are having a check-up a week or so later.

I will use the shorthand 21-week visit, although sometimes the gestation is closer to 20 weeks, 24 weeks or anywhere in between. I'll talk about our two patients, the mother and the fetus. I'll talk about three tasks, checking the details of the mid-trimester ultrasound scan, updating vaccines and reviewing previous screening tests from earlier in the pregnancy.

Finally, every visit provides opportunities for health education, checking on psychosocial wellbeing and pre-empting the patient's question about what next. When will she come back to antenatal clinic and what are the other steps she should take for a healthy pregnancy, birth, baby and early parenting?

Taking our number one patient, the pregnant woman. Everyone is different, but many women enjoy second trimester. They have a reprieve from some of the annoying first trimester problems such as nausea, vomiting and fatigue. Nevertheless, do keep listening and evaluate any symptoms as you usually would with a careful history and problem-oriented examination.

Even in the absence of symptoms, don't forget the examination, which is to take the blood pressure and to examine the patient's abdomen. When you do the latter, you'll find the uterine fundus is palpable just above the umbilicus at 21 weeks. You won't really be able to feel fetal parts. If you use a handheld Doppler in the midline between the umbilicus and the pubic symphysis, you can usually hear the typical fetal heart rate at 110 to 160 beats per minute.

Concerning our other patient, the fetus. The woman, you and society are increasingly recognising this as a separate entity now that pregnancy has advanced into its second half. The woman can probably feel fetal movements now. Just flutters, not very strong, but something from about 21 weeks in a first pregnancy and around 19 weeks in the second and subsequent pregnancies, although there is a range of normality concerning the first time a woman notes fetal movements. The old-fashioned term for this milestone in pregnancy is quickening.

So as discussed in the examination findings previously, the uterus is now an abdominal organ reaching the woman's umbilicus or a bit above. And so women note they're more comfortable in loose-fitting clothes and may say they're starting to show their pregnant belly.

From a legal perspective, births after 20 weeks are registrable in Victoria, Australia. The likelihood of surviving infancy increases if birth is 22 weeks or later. But at the time of this podcast recording, births at 20 and 21 weeks, although registrable, don't realistically lead to survival beyond minutes or perhaps hours.

From a healthcare service perspective, some hospitals start using birth suites as an urgent assessment centre rather than the emergency department if a woman has reached 20 or more weeks. So, GPs provide a great deal of general healthcare, but some women also seek out healthcare at hospitals and they will be directed to the birth suites even if their symptoms are more to do with the flu, coughs, colds or trauma because they're now in the second half of pregnancy. They are also assessed urgently for more standard obstetric complaints such as contractions, vaginal discharge or reduced fetal movements.

Okay, three technical tasks for the 21-week visit. The first technical task is to very carefully check over the morphology ultrasound scan report with the woman. Of course, the baby's the star player in the ultrasound scan performance, but don't forget the less glamorous but still important parts of the ultrasound examination. Check particularly descriptions of placenta, cord, amniotic fluid and cervix.

So, concerning the placenta, the report will tell you if the placenta is implanted fundally, which is in most cases (95%) or low-lying in 5%, meaning that the placental edge is two centimetres or closer to the internal cervical os. If the placenta is low-lying, then this should be checked in later pregnancy around 32 weeks or earlier if the woman presents with an antepartum hemorrhage.

Many placentas which are low-lying before 20 weeks are later in the upper segment because the lower uterine segment grows as the pregnancy progresses. And this is good news, that the previously low-lying placenta is no longer placenta previa by the time of childbirth. That's the placenta.

Now concentrating on the cord, it is really important to check where this implants into the placenta. Healthy implantation is usually somewhere into the central bulk of the placenta. By contrast, an edge insertion is called marginal, and if the cord runs through the membranes without Wharton's jelly protecting it, this cord is called velamentous.

Both marginal and velamentous insertions can sometimes have associated vasa previa, meaning fetal blood vessels which are prone to rupturing with terrible, dire consequences. So knowing about cord insertion is really important to help us work out if vasa previa is an actual risk.

So it was placenta and cord. Moving on to the other non-baby thing is the cervix. Concerning the cervix, the longer is better in the mid-trimester from the point of view of predicting premature birth. If it's short, meaning less than 35 millimetres when measured through the woman's abdomen, or less than 25 millimetres when measured more accurately transvaginally, this shortness means you should ask for an obstetric opinion about more accurately predicting preterm birth and what measures can be used to prevent preterm birth.

OK, moving to the baby now. Well, fetal number and dating should be checked and reported on. Most of the woman has had previous scans, so the 20-week scan shouldn't turn up too many surprises about unsuspected twins or wildly different expected due date.

But if this is the woman's first scan in pregnancy, then we use fetal size to check against what would be expected from the duration of amenorrhoea or any other information about pregnancy duration. And all this is put together to clarify a likely expected date of confinement or EDC. This should be decided on by 21 weeks and not changed again later.

OK, then moving to more detail about the baby. The woman and her maternity caregivers are understandably concerned about whether the fetus is normal. And a lot of time during the ultrasound scan will have focused on various views of the developing fetal anatomy.

So ultrasound is highly accurate for finding out some problems, anencephaly and spina bifida are some examples. Conversely, it's highly inaccurate or actually never realistically detects some other problems before birth. So in 2022, I'd say no cases of congenital dislocation of the hip or undescended testes are detected before birth.

And then there are other conditions which are detected to some extent. Many but not all cases of congenital heart disease, cleft palate or club foot are detected before birth. So for many women, the next opportunities to address their concerns about “is my baby normal” are actually much later after the child has been born, is being assessed clinically and with screening tests for hearing, post-ductal oximetry and blood spot screening for inherited metabolic conditions.

So the time of recording, Victorian 2022, women generally don't have a routine third trimester ultrasound scan unless they're clinically indicated. But it has to be said that the clinical indications are fairly broad. So it works out that over half of women do have another scan after their morphology scan. These scans are mainly aimed at ruling out fetal growth or amniotic fluid anomalies. But as a side issue in a few cases, occasionally an unsuspected fetal anomaly is discovered, probably around 1% or fewer cases. Okay, so that's the first technical skill is going through that morphology ultrasound in a great deal of detail.

The second technical task at the 21-week visit is to update the woman's vaccine history, especially about three non-live vaccines, pertussis, COVID-19 and influenza. So 21 weeks is the usual time for a pertussis booster. The boost is given as part of a triple antigen, single needle, but with antigens which promote immunity against pertussis, tetanus and diphtheria. The pertussis is the main component of interest and the purpose is for the woman's immune system to mount a boosted antibody response with enough time to produce mature immunologically avid antibodies, which cross the placenta and protect the baby after the baby's birth from having a severe pertussis infection, especially in very early infancy, since babies younger than six weeks can't have their own vaccination against pertussis.

Now it is safe to give pertussis later in pregnancy. It just seems to work better if it's given some time for the immune response to mature before the baby's actually born. In countries without a universal tetanus vaccination program, targeting pregnant women helps protect them and their young children from tetanus too.

Incidentally, in a highly vaccinated setting, such as Australia, non-pregnant adults, such as fathers of the baby, grandparents, healthcare workers, only need their pertussis booster every 10 years. But the adults with a placenta, meaning the pregnant women, warrant having a booster every pregnancy as the woman is the conduit of antibodies to her unborn child.

The other two vaccines, COVID and influenza, are important because both COVID and influenza infections are worse for women in advancing pregnancy than in women who are not pregnant. And that's probably because pneumonitis is challenging, particularly when a woman's diaphragm is compressed by the third trimester uterus, and also because a pregnant woman has to meet respiratory demands both for herself and her unborn baby.

COVID and influenza vaccines are safe at any stage of pregnancy, but they're arguably most important to be provided before pregnancy advances into the third trimester. So 21 weeks is a good time to have these vaccines, if not previously given. So we've talked about the ultrasound review, the vaccine review.

The third technical task is to check and document results from other previous screening, blood and urine tests, the sort of things which you've covered off in the learning materials, webinars, etcetera, about the booking visit. So check, document, and clearly act on any anomalies. So most antenatal clinics have systems in place for this, but I would say it's always a good idea to include the pregnant woman in this task, give her copies or write in her handheld record.

And you can assure women that having had all those blood tests early, most women don't need any more blood tests until 28 weeks, and that'll be discussed in another podcast. So after those three technical skills, finally we come to the more generic skills. We need to try to meet the woman's health education needs, and this is an ongoing process.

Depending upon the woman's curiosity and needs, you might end up discussing diet, exercise, work, sex, relationships, exposures, birth, and early parenting. And you might also share in this education by referring the woman to multidisciplinary experts. So the 21-week visit and this podcast is coming to a close.

Towards the end, you need to sketch out with the woman what happens next, and most women will have their next visit at 28 weeks. There are podcasts in development or published about antenatal visits at other milestones, 28, 36, and 41 weeks, and a podcast about the non-milestone visits or the in-between visits.

So I hope you enjoy antenatal clinics. Seek out those 21-weekers and everybody else, that you will enjoy meeting pregnant women and the antenatal team and participating in various tasks along women's pregnancy journeys. Thank you.