Portuguese term (edited): sem car�ncia

The meaning of "sem carência" in your sentence (comprar algo sem carência), leads me to believe that "carência", in this case has the meaning defined in 2 by Aurelio dictionary, look:

[Do lat. vulg. carentia, do lat. carere, 'ter falta de'.]
S. f.
1. Falta, ausência, privação: Ex.: Durante o cerco, a cidade sofreu a carência de víveres.
2. Necessidade, precisão: Ex.: A criança tem carência de afeto.
[Sin., (acepç. 1 e 2): carecimento.]
3. Econ. Período entre o recebimento de um empréstimo ou financiamento e o início de sua amortização: Ex.: O pagamento do empréstimo será em 20 prestações mensais após dois anos de carência.

Meaning 3 is what you asked about "Plano de Saúde", but has nothing to do with the sentence "comprar algo sem carência" (comprar algo sem necessidade).

Here's what the Babylon says:

needlessly
adv. sem necessidade

Portuguese term (edited): sem car�ncia

If a group health plan provides coverage to you through an HMO with an affiliation period, the affiliation period cannot be longer than 2 months (3 months for a late enrollee) from your enrollment date, and the plan cannot impose a pre-existing condition exclusion. During the affiliation period, the plan cannot charge you premiums, and the HMO is not required to provide benefits.

The affiliation period must run concurrently with any waiting period for coverage under the plan.
http://www.dol.gov/elaws/ebsa/health/4.asp

Massachusetts law also allows your insurer to impose a waiting period regardless of whether you have a pre-existing condition. A waiting period can be imposed for up to 6 months from when your coverage begins during which time you will pay premiums but will not receive coverage for non-emergency services.
http://www.healthinsuranceinfo.net/ma02.html