I have heard of this remarkable occurance and I'm pretty sure that the stories were all about women who were fairly obese as that is the only possible way that I can think when you wouldn't know you were pregnant. I've been pregnant 3 times now and have known I was pregnant before I even missed my period.
MY OWN EXPERIENCES
The first time sadly ended in miscarriage fairly early at about 5 weeks, but even at that early stage I knew that I was pregnant. It took me 3 weeks and a scan to convince even the doctors that I was pregnant as the tests all came back negative! I don't know what it was, I just knew. My period wasn't even late, because I was miscarrying I was bleeding so I couldn't even say that!
With my second pregnancy it was the same, a week before my period was even due I just had this strange feeling that I was pregnant. I waited another 2 weeks before taking a test and that happily came back positive. I can understand how at this early stage women can be unsure, as with all my pregnancies I have bled slightly. My periods are extremely erratic so had I not proved that I was pregnant I suppose I could have put it down to stress or just irregular periods. However, I got to 14 weeks and I could definately feel the baby move. Not just the slightly 'popping' movements that feel a bit like gas, but actually kicks. 2 weeks later I started having Braxton Hicks contractions, where the womb tightens to practice for labour and there is no way I could have missed these! I was always very disappointed with my bump as I didn't put on much weight, in fact I lost weight initially, but even without the huge stomach it was still blatantly obvious that I was carrying!
I could put these two experiences down to the fact that my husband and I were trying for a baby so I was definately certain that there was a chance of pregnancy happening! But, with my third pregnancy, the one I am expecting as I write this, it was a complete surprise. We'd been using protection so as far as we were concerned there was only that 'legally written 3% chance' that all the condom manufacturers have to put on the box.
Again, my period wasn't late, in fact it was perfectly normal - a little light spotting followed by some intense period-pain followed by a large bleed. But, I 'felt wrong'. I can't explain it, especially to someone who has never had a baby, but it was like a maternal instinct. I took myself to the doctor, wondering if I may have a urinary infection and whilst I was there I said, half jokingly, perhaps I was pregnant again! They did a test and it came back positive. For the first 18 weeks of my pregnancy it would have been easy to miss - I didn't put on any weight, I was still having periods of bleeding, and I didn't feel any movement. Even now at 23 weeks the kicks are nowhere near as big as they were with my daughter, although I am now starting to get a bump!
SYMPTOMS YOU CAN'T IGNORE
As women can bleed throughout pregnancy and not put weight on it might be easy to mistake the early symptoms for something like a urinary infection, however as the pregnancy progresses there are symptoms you just can't ignore.
*Movement - the first few kicks just feel a bit like trapped wind, but how can you ignore a foot hooked into your ribs or an elbow in the kidneys?
*Braxton Hicks - usually these don't hurt and can easily be ignored, but the further on you get, you will start to feel your stomach become hard and tight for a few moments at a time.
*Cravings - they don't have to be unusual, but during the second trimester of pregnancy you do start craving more food.
*Excessive urination - at first it's the hormones, but once a baby starts putting pressure on your bladder you will find that you need the toilet more often. There will be no sign of urinary infection though.
*Nesting syndrome - as you reach the third trimester the maternal instinct kicks in and you will begin to want to tidy up and bake lots, getting your 'nest' ready for the baby's arrival.
So although I can see why women would say that it is easy to miss a pregnancy, I really don't know how they could! It's not just lack of bleeding and kicks that prove you are pregnant. There is just a miraculous feeling that overcomes you during pregnancy getting you ready for parenting. As I've said, before the symptoms have even started I've known that I was pregnant.