For many years, the standard timing of contractions and when to go to the hospital was 5-1-1. That basically means that when your contractions were five minutes apart, last about a minute, and you had them for about an hour or two. If you went to the hospital sooner, you were often sent home, or for a walk. This was all based on the theory that with contractions spaced to that degree, you would be at the beginning of active labour, or approximately three to four centimeters dilated. But a few years ago, the American College of Obstetricians and Gynecologists- and more recently, the Society of Obstetricians and Gynecologists of Canada- re-evaluated when active labour started. The new bench mark for active labour is now five to six centimeters dilation. The study this change was based on can be found here, and was prompted by a desire to lower primary cesarean births.
As such, going to the hospital when things hit 5-1-1 now meant that you weren't admitted right away ,and were left wandering the halls of the hospital to "speed things up". Therefore, we need consider a new hallmark for when to go to the hospital. 3-1-1 is now more commonly used. This translates to when your contractions are 3 minutes apart and lasting about a minute for approximately 30 minutes to an hour. This should put you at about five to six centimeters dilated, which is when you'll more likely be admitted, and is a good time to get an epidural if you're choosing to have one. Getting to the hospital any sooner doesn't get you a baby any faster. Rather, it's more likely to get you more medical interventions to speed up labour.
However 3-1-1 is merely a guideline. There are several things that will need to be considered when deciding when to go to the hospital. The first will be if you've tested positive for Group B Strep, a common harmless bacteria that can occur in most adults. However if it's present close to the time of delivery, it can be harmful to newborns. The risk of your baby coming ill however is about 1 in 2000. But because the risk exists- even though it's small- in Canada and the U.S., labouring parents will be given IV antibiotics every four hours until the baby is born. So with this protocol, most hospitals will want you to come in sooner to ensure you get several doses of the antibiotic beforehand.
The second thing to consider when deciding to go to the hospital is your own medical history. There maybe something there that may require you to come to the hospital sooner so you can be monitored more closely. Having a discussion with your care provider and asking lots of questions will help you both come to a mutually agreeable decision on when would be the best time for you to be admitted.
Thirdly, you will need to factor in your drive time. If you live an hour or more away from your place of birth- or if rush hour traffic is going to be a major factor- I'm sure you won't want have to deliver your baby at the side of road. So if your drive in is going to take an hour or more, consider adding one or two to the first number of 3-1-1. Consider 4-1-1, or even going back to the original 5-1-1.
The next consideration is if this is your first baby- which takes longer, or a subsequent birth- which will normally be shorter. For your second or more babies, you'll definitely need to go back to 5-1-1 or more, as early labour tends to be shortened in subsequent labours.
Finally, if you feel like you need to go to the hospital- regardless of what your contractions say- then you need to go. Most times your gut instincts are a better register of when to go to the hospital than anything a book or the internet has to say. Hospitals would rather you be safe than sorry. The best case scenario is that you get there too soon. The worst case scenario is that you don't go when you feel you should, and you end up having your baby in front of morning commuters.