Sunday, 23 October 2011

When is my due date?

Working out your baby’s due date is simple – and complex!  On average a pregnancy last 40 weeks from the first day of the last menstrual period (LMP) – or 38 weeks from conception.  Length of pregnancy is counted from the LMP, so four weeks after your LMP you would be counted as being four weeks pregnant even though you probably only conceived two weeks ago.  If you know when your LMP was, the easiest way to work out your due date is to go through the calendar counting forward in weeks till you get to forty weeks.  So if your LMP was on a Tuesday, then your due date will be on a Tuesday.  Counting 38 weeks from conception is more accurate, if you know when it was, especially for women who do not have regular 28 day cycles.

Health care professionals do not have time to count through the calendar so they use one of two ways to quickly calculate your due date.  The first is a wheel which has dates of the year on the outer wheel and the weeks of pregnancy on the inner wheel.  By matching 0 weeks on the inner wheel to the LMP date on the outer wheel, the corresponding due date at 40 weeks can be read off.  These wheels are also used to work out how many weeks pregnant you are at check ups.  These wheels are not very accurate and can be out by a day or two.

The other way is to take the LMP and add on nine months and seven days; for example, LMP 7 Jan gives a due date of 14 October.  Again this is an approximate measure and can be out by a day or two: in 2011 7 Jan is a Sat and 14 Oct is a Sun.

The first scan routinely offered in the UK is a dating scan, at about 12 weeks.  This is used to confirm a due date from LMP or to work one out if LMP is not known (as well as some checks for abnormalities).  It does this by measuring the length of the femur, I believe.  At this point in the pregnancy there is a good correlation between this measurement and predicted due date.  As the pregnancy progresses it is harder to assess gestation in this way as babies growth varies.  Later scan are less reliable in predicting size of baby too.  Research has shown that due dates from dating scans are more accurate than from LMP.  If, from this first scan, the due date calculated is more than a week different from that from LMP it is likely that the health professionals will change the EDD.   This can be confusing – for one of my friends it meant that, by the scan dates, she would have conceived when her and her partner were in different countries!

How can there be such discrepancies?  Of course she could not conceive without a partner and scans are only approximate.  It cannot be an exact science.  Women have varying lengths of menstrual cycles and do not all ovulate on day fourteen of their cycle.  Many women have unpredictable cycles.  Sometimes events in a person’s life can cause ovulation to happen earlier or later than usual.  You can decline the scan.  If you are sure of your dates then you do not need it to confirm this.  If you do not know your LMP and would like a scan to give you a due date then you can ask them not to check for abnomalities if you don't want to know (at this scan the nuchal fold is measured which is a marker for Down's Syndrome).  I had no routine scans with my last two - more about that another time - but with my last I had bleeding, at 12 weeks, that did not lead to miscarriage so I attended an Early Pregnancy Unit.  I was offered a scan to confirm life but I asked for no abnormality checks to be done, including nuchal fold.  This was written onto my notes and respected.  With all of my pregnancies I had decided not to take any abnormality screening, including triple test - but this is purely a personal choice that every couple must make for themselves.

However a due date is calculated – by calendar, by wheel, by rough approximation, or by scan – a due date is only an approximate date for baby’s arrival; in fact it is often written as EDD (estimated due date or estimated date of delivery).  Only 4% of babies arrive on their due date and ‘term’ is defined as any time between 37-42 weeks, so the baby could come any time 3 weeks before that date or up to 2 weeks after and still be considered normal – and some babies come earlier than 37 weeks and some later than 42!

So does it matter?

At the beginning of the pregnancy it is hard to imagine that one or two days difference in a due date matters.  We all like to have a date to consider.  We also have a tendency to wish the pregnancy by and want the baby to come as early as possible.  However, it is worth going with the latest due date from one of the methods – if the date given by midwife/gp/scan is later than from counting through the calendar, then keep quiet; but if it is earlier then insist on using your date.  By having a later due date you give yourself a bit more time and at 41 weeks every day will count.  You will feel pressure from yourself and others for the baby to come.  (Some women choose to tell family and friends that baby is due ‘sometime in June’ rather than give a specific day.)  Also in this country it is routine to offer induction to women to start labour off at 10 or 12 days after the due date.  Induction can result in a more painful labour and is associated with a higher use of epidural and assisted birth (forceps/ventouse).  If induction methods fail to get labour going or progressing then women will be given a caesarean.  So the later your due date, the less pressure and worry on you – for a day or two – which could be all that baby needs to come on its own.  (Of course you can decline induction – you can wait and be monitored.) 

And then you wait ...

Of course all of this has no bearing on when your baby will actually be born.  If anyone invented a way of giving women due dates that were accurate even to a day or two then they would be rich; instead we have to put up with not knowing and a 5 week window, which even then isn’t definitive.  Baby chooses the day – and from my experience babies want you to know from the start who’s in charge – them!

Pregnant? Now what?

So you’re pregnant?

Here are some things you should know straightaway...

How do you know you’re pregnant?
·         the most obvious is that you have missed your period
·         feel extremely tired
·         Breast changes: areola (dark area around your nipple) darkens, breasts swell, breasts are tender, glands (like spots) around the edge of your areola enlarge (they are called Montgomery tubercles)
·         Feel hormonal, like the start of your period; some women even feel period like aches.
·         Metallic taste in mouth
·         A positive pregnancy test: these are extremely accurate and if you have used one your gp/midwife will not do another.

What now?

Well – you could do nothing.  There is no need to see anyone or do anything.  If you don’t see anyone or have any checks your baby will grow and one day you will go into labour and your baby will be born – it’s nature, it’s what humans and cats and dogs and pigs and all other mammals have been doing for millenia.  However, antenatal screening has been shown to be beneficial – but it is up to you to choose which parts of it you want for you and your baby.  No test can guarantee a healthy baby, and you can’t jinx your pregnancy by not doing a test.  There are reasons for doing each test and check up, and you should weigh each up and decide.

Most people in the UK tootle off to see their GP or contact a midwife.  It has become more common in recent years to contact a midwife directly – you can get the details from your local surgery or contact the maternity unit at your local hospital.  There is a poster up in my local surgery and children’s centre with the number.  They will just want your name and contact details and the date of the first day of your last period – pregnancies are measured from this date which is often abbreviated as LMP (last menstrual period).
If you do go to a GP: they will want to know your LMP and will calculate your estimated due date (EDD, also known as estimated date of delivery).  (See next blog post for how this is done.)  They may check your blood pressure and listen to your heart.  Mostly they will just fill in a form to send off to the midwife.  They may ask you where you want to have the baby.  This is only so they know who to send the paperwork to.  You could ask what the options are in the area – choice of hospitals, any birth centres?  Most GPs have very little firsthand experience of birth so you may find the midwife is the best person to ask anyway.  It is perfectly reasonable to say ‘we haven’t decided yet’.  You can make a decision about place of birth, or change your mind, at anytime – even during labour!  Bear in mind, home birth is an option for first timers – in fact the first is often the best to have at home (see my blog post, first baby at home).  Sometimes GPs try to put women off homebirth or say it isn’t an option, but, again, they have little experience of birth, beyond a short time during their training.  It always strikes me as bizarre to be asked where you’re having the baby at a time when the main worry is whether you’ll miscarry, and you know so little about what birth is like and how your pregnancy is going to progress.

If you contact a midwife directly then you will not need this first appointment and will go straight to a booking visit.

Booking visit

Your midwife will contact you to arrange a booking visit.  These are usually done in a woman’s own home by a community midwife, at about 8-10 weeks, and last about an hour.  There is a lot of form filling and some discussions.  They will go through
  • Your contact details and your partners’
  • How and when to contact a midwife
  • Your medical history
  • Options for place of birth
  • Programme of antenatal checks, inc scans
  • Information about the benefits of breastfeeding especially straight after birth
  • Healthy pregnancy – diet, exercise, what to avoid, smoking, drinking, domestic violence

They will probably test your urine (they may give you a pot with a lid to keep so you can bring a sample of urine to each check up).  Urine is tested for levels of protein and sugar which can indicate potential problems.  They may take your blood pressure to give an early reading to compare later measurements to.  They may ask to weigh you, or ask you for your weight and your height, and thereby work out your bmi.  As with all tests you choose to accept or decline each.  Even though they are routine, there is no obligation to accept.

The midwife will be taking your details down twice – one in a set of notes you will be given to keep with you and bring to appointments and one kept by the midwife at the hospital.  You will be given a date for the first scan if you decide to have it, or the midwife will make an appointment for you and contact you later.  You will also be given an appointment for a blood test (or you’ll be asked to make one at your surgery). 

Further antenatal check ups will take place either at your gp surgery, children’s centre, hospital, birth centre or at home.  For more details of what is done at each check and how many to expect you can look at the national guidelines by NICE (National Institute of Health and Clinical Excellence – also see their guidelines on caesareans, anti d, care in labour and more).  Here is the link for the antenatal care guidelines.  They will send you a free copy of their patient copy or the professional’s version or you can view on line.

I hope this helps.  Early accessing of maternity care (contacting a midwife and starting antenatal checks before 12 weeks) is associated with improved outcomes.  If you are a first time parent then you are probably excited about the whole process – as I was.  By the time I was pregnant with number 3, 4 and then 5 I was much more laid back and didn’t contact the midwife till later.  With baby number 4 I was 17 weeks and with baby number 5 I was 16 weeks at my booking visit – but then I didn’t want any scans and knew that my previous pregnancies had been uneventful.

Early pregnancy units

Just a quick note before the end of this post.  Most hospitals have early pregnancy units.  If you think you are miscarrying you can just let nature happen.  However if you are bleeding and there is no sac, or if bleeding and pain continues, or you would like to know more you can ring up and make an appointment to go there.  If the pregnancy is at least 14 weeks they may be able to hear a heart beat.  They also offer scans. More pregnancies than you’d think have episodes of unexplained bleeding with no miscarriage.  (See previous post for more information about miscarriage and sources of support and information.)