I've read What is the least problematic age difference between siblings? but I had a different question.
That question is rather "from a child's point of view: what age would you prefer your siblings to have".
Mine would rather be:
The March of Dimes website had this to say:
How long should a woman wait between pregnancies?
For most women, it’s best to wait at least 18 months before getting pregnant again. This gives a woman’s body enough time to get ready physically for another pregnancy. It also gives her time to adjust to life as a mom. Shorter time intervals between pregnancies may increase the risk of premature birth (8). However, not all women can wait 18 months because of their age or other reasons. A woman should talk to her health care provider to determine the right amount of time for her.
Babycenter has advice for moms who deliver via vaginal birth and via Caesarian section
There's also an entire thread on TheBump with numerous users chiming in with their experiences with their doctors, their children, and so forth.
(As an aside, you can be intimate with your partner far sooner than the recommended 18 months!)
In my opinion any 'advantage' of an immediate pregnancy can also be a 'disadvantage'in the right situation. For example:
However, they can't share a crib/toddler bed, which means you have to have 2 of everything, costing more money - disadvantage (unless you co-sleep). When they're older they can share bunk beds (assuming same sex kids), etc.
However, training 2 kids at nearly the same time can be....frustrating - disadvantage.
Having 2 kids go through that period at the same time... disadvantage.
However, trying to juggle breastfeeding 2 babies at once: a newborn that's clusterfeeding every half hour and a 10 month old that is hungry and/or wants to comfort nurse - disadvantage if you can't get a good feeding schedule going.
As far as time between pregnancies; in my opinion there should be at least 9 months between them. Pregnancy is very taxing on a woman's body and back to back pregnancies even more so. The uterus needs time to contract, the same with the muscles and ligaments which have stretched to support the stomach.
It seems to me this is likely to be a matter of personal preference and entirely dependent on your situation (after 18 months that is). I've known of families with siblings as many as 11 years apart for whom it worked really well and others that wished the kids were closer in age) I've also known of families whose kids were as close in age as could be (one was even EXACTLY one year apart - the second one was a "surprise" but most people think the girls are twins). It is the same story with these families, some are glad for the closeness in age and some wish their kids were further apart in age.
Things like emotional closeness or not-such closeness of siblings seems to have more to do with how they are raised, who they are naturally as people and how much they have in common in terms of interests than it does age.
As a previous answerer pointed out, many advantages of certain age differences also come with disadvantages.
I guess I'd suggest that after being sure you are making a choice that considers your own health (at least 18 months between) as shown in this answer, don't worry about it too much and plan based on what your priorities, financial situation and wishes dictate. Make your decision and then don't question yourself too much (we tend to do that too much as parents anyway).
In a recent study conducted by the Journal of the American Medical Association, the ideal waiting period for in-between pregnancy is 18 months to two years. Studies reveals that women who get pregnant right after having a child or women who waited many years to have another child have the greater risk of having serous delivery-related complications like low birth weight and or premature birth.
Based from their study, women who conceived less than six months of giving birth had 40% increased risk of having premature baby and 61% increased risk of having low birth weight, as compared for those who waited 18 months to two years in between pregnancy.
Meanwhile, mothers who waited at least five years to have another child had 20% to 43% of having babies who are either born prematurely or having low birth weight. Pregnancy Spacing Affects Outcome.
